London now
Almost every cuisine in the world is represented in London, from quality Italian cooking at The River Cafe out in Hammersmith, (in the suburbs you will sometimes find "Italian" restaurants whose association with Italy is far in the past) through Chinese in Soho and curry almost everywhere. <Central London curry houses>. There's no guarantee of authenticity of course. I note some Americans expect to find good Mexican food, which is probably the last thing to look for, although there are one or two to be found. My advice is not to look for ethnically themed places at all, many of the best places now serve what can be best called "modern British" or "modern European" cooking, interpretations of some traditional dishes along with new creations drawing on food cultures from all over Europe and further afield.
Restaurants are constantly changing so either a good eye for a restaurant or a guide book are essential. In Spain or Italy, for example, you are unlikely to get really bad food anywhere except a few tourist traps, but in London take a little more care. I always avoid chain restaurants, places with laminated menus that don't change with the season, smells of cheap cooking oil and "chips with everything" establishments. If you're looking for something cheap (London isn't a cheap town) try a pub or a sandwich bar. I never eat in burger bars, cheap kebab shops or from street hot-dog vendors. In the upmarket restaurants in places like Charlotte Street you will often find offers available if you are willing to eat at lunchtime rather than dinnertime (lunch starts at about 12 noon in London and dinner is at 8 pm although traditionally people may eat as early as 6 pm. Recently it has become much easier to eat later but don't expect to be able to sit down at midnight. 
Restaurant bills may have service already added, if not you may wish to leave a discretionary tip of about 10%.
Dress codes
In the top end hotels and restaurants you may find some places that require men to wear a jacket, a tiny number of places also insist on a tie. The Ritz is one that insists on the latter. La Gavaroche on the former (2005) Both have items they will lend you. The number of these establishments dwindles each year. (I have never worn a tie to a restaurant in my life, DJ (tuxedo) occasions aside. 
"Smart casual" is fine everywhere else. Leather shoes, chinos and a shirt, plus a jacket if you feel it's a smarter place.
Sleeveless vests and shorts may be frowned on but will probably be allowed, but don't believe you are fitting in. The same applies to a lesser extent to jeans, trainers and track suits. (Although jeans may not be regarded as the thing to wear in smart places, don't believe the old myth that wearing them is going to mark you down as an American).
In pubs and modest restaurants anything goes except that bare chested men will usually not be served.
Beware of pubs that have a no trainers/jeans rule and a doorman to enforce it, this is more likely to indicate rough customers than the opposite. The same goes for a pub displaying an "Over 21 only" sign. 

"Soho" sounds like a Chinese word but is in fact named after an old hunting cry.
 

Jamaica patty and brown fish with rice and beans

Some central London curry houses:-
Benares Berkley Square W1<website>
Bombay Brasserie Courtfield Close SW7 (£££)<website>
Cafe Lazeez 21 Dean Street W1<website>
Cafe Spice Namaste 16 Prescot Street E1<website>
Caravan Serai 50 Paddington Street W1
Chor Bizarre 16 Albermarle Street W1
Chowki 2-3 Denman Street Piccadilly W1
Chutney Mary 535 Kings Road SW10 (£££)<website>
Cinnamon Club Great Smith Street SW1 (£££)<website><cookbook>
La Porte des Indies 32 Bryanston Street W1 (£££)<website>
Malabar Junction 107 Great Russell Street WC1 <website>
Palms of Goa 12 Charlotte Street W1
Rasa Samundra 5 Charlotte Street W1 (fish)<website>
Red Fort 77 Dean Street W1 (£££)<website>
Salloos 62 Kinnerton Street SW1
Soho Spice 124 Wardour Street W1
Tamarind 20 Queen Street W1 (£££)<website>
Quilon 41 Buckingham Gate SW1 (£££) <website>
Veeraswarmy 99 Regent Street W1 (£££)<website>
Zaika 1 Kensington High Street W8 (£££)<website>

(£££) at expensive end of scale

If you get away from the centre to Bromley or Bexley (SE), do try:- 
Tamasha Restaurant & Hotel
131, Widmore Rd
Bromley Kent BR1 3AX
Tel: 0208 460 3240
(Bromley North station, double room £65 (2003) )
<website>
An elegant if expensive restaurant in the top 100 UK curryhouses, redolent with memories of the raj. I recommend trying the fish or seafood dishes and do finish your meal with Tamasha special coffees (min 2 persons) expensive but spectacular!
 

The British Curry

The CAMRA Good Beer Guide 2008.
35th edition. 4,500 of the best pubs throughout the country serving good beer selected by CAMRA's 77,000 members (no listing fees accepted) plus beer, breweries and beer festival listings. Listing of pubs of significance to national heritage. Prize winning beers of the year. Edited by Glenfiddich award winning Roger Protz 

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Eating out in pubs - Michelin
Good food in informal surroundings.
The British pub has been transformed over the last twenty years. Once a place to drink good beer, play darts or dominos and chat, the arrival of the car as the usual means of transport at first opened up many rural pubs to new visitors. But the realisation that drinking and driving didn't mix then left many in crisis. Beer had often reached a low point with second rate "keg" substitutes for the real thing and no food. Luckily enterprising landlords soon realised that things must change and the modern pub emerged, selling good "real" ale alongside good food. When this guide clattered through the letterbox, it only took a few minutes to see they had found most of the classics, pubs that it had sometimes taken me half a lifetime to stumble across, others I used to play darts in after work, that I learn with surprise are now serving good food rather than crisps.
Each pub gets a page, with a colour photograph, contact details, facilities and brief directions.A box indicates which real ales are served.(Its sad to see, from an English point of view, that the Irish pubs still generally have no real ale, oh for a pint of "real" Guinness) Food serving times and prices are given and then there is a pen portrait of the pub and its food along with typical dishes. 
This is the first edition of this guide, long may it continue! 
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The Gastro pub cookbook - Diana Henry
150 of the best dining pubs in Britain and Ireland.
20 gastropubs dealt with in detail with atmospheric black and white photos of the regulars along with colour photos of the pub locations and the food. Recipes from the featured pubs are usually at the "comfort-food" end of modern british cooking. Things like smoked haddock with poached egg and mustard sauce, shepherds pie or lamb shanks with harissa on pea couscous.

The London Pub Haydon
115 pubs from the East End to Soho. The pubs origins, architecture and character with photos of interiors and exteriors. An ideal starting point for a pub crawl round some of the best pubs in London and a nice souvenir for the visitor. Practical information with location maps, opening hours and food and drink.There are many interesting pubs in London but some of the best are hidden away, although only yards from busy roads. Do you know which pub is on both sides of a street connected beneath the pavement? 
Which pub has written above the bar "Meum et propositum in taberna mori vinum. Sit appositum marlentis ori, ut decunt cum venerint angelorum chori. Deus sit propitus huic potentori"? "To die in a tavern is my definite plan, with my mouth to the tap as close as I can, that the angels would say when singing began: O Lord show mercy to this boozy man".
Which pub used 50 types of marble in its construction?
Which pub, founded in 1583, was the model for "The Six Jolly Fellowship Porters" in Dickens's "Our Mutual Friend"?
You would if you owned this book!

 
 
 

Some classic London pubs The Champion 13 Wells Street W1 The Coal Hole 91 Strand WC1 The Cock 27 Great Portland Street The Lamb & Flag 33 Rose Street WC2 The Ship & Shovel Craven Passage WC2 The Grapes Narrow Street E14 The Lamb Leadenhall Market EC3 Punch Tavern Fleet Street EC4 Ye Olde Cheshire Cheese Fleet Street EC4 The George Borough High Street SE1 The Mayflower Rotherhithe Street SE16 The Trafalgar Tavern 5 Park Row SE10 The Dove Upper Mall W6 The Prospect of Whitby Wapping High Street

CAMRA listed interiors The Black Friar Queen Victoria Street EC4 The Olde Mitre Ely Court Citte of York 22 High Holburn WC1 The Princess Louise  208 High Holburn WC1 The Salisbury St Martins Lane WC2 The Black Lion Kilburn High Road NW6 The Red Lion Duke of York Street SW1 The Argyll Arms Argyll Street W1 The Windsor Castle Campden Hill Road W8 Warrington Hotel Warrington Crescent W9

Food specialists The Eagle  Farringdon Road EC1 The Oak  Westbourne Park Road W2 The House  Cannonbury Road N1 The Duke of Cambridge St Peters St N1 The Highgate Highgate Road NW5 The Drapers Arms Barnsbury Street N1 The Ladbroke Arms Ladbroke Road W11 The Well St John Street EC1 The Fox Paul Street EC2 The Pilot 56 Wellesley Road W4 The Cow Westbourne Park Road W2 The Anglesea Arms Wingate Road W6 Ealing Park Tavern South Ealing Road W5 Anchor and Hope The Cut Waterloo SE1 The Waterway Formosa Street Bayswater W9

More pub books

Wine bars
The number of wine bars grows daily, on average they will tend towards better food with less of the hubbub of a pub.

Fish and Chips
A few central London chip shops. Note that the fish market is not open on Sunday/Monday so avoid those days.
Fish Central 149 Central Street Barbican EC1
North Sea 7 Leigh Street WC1
Rock and Sole Plaice 47 Endell Street WC2
Fryer's Delight 19 Theobolds Road WC1
Golden Hind 73 Marylebone Lane W1
Sea Shell 49 Lisson Grove NW1
Seafresh 80 Wilton Road SW1
Masters Super Fish 191 Waterloo Road SE1
 

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(Illustrations copyright and courtesy of owners)
Time Out Eating and Drinking Guide 2004
Good general food and drink guide by London's leading listings magazine, organised by type of food, with maps.

Rough guide to London restaurants 2004
320 London restaurants reviwed by award winning author.

London pub guide - CAMRA
Pubs recommended for good beer by the members of the Campaign for Real Ale.