Having a night out in London can be fun but expensive and a touch depressing when you go through ATM/bank slips in the morning and realise the cash you had has been replaced by coins and paper receipts.
Know the Cheaper pubs: Pub chains such as Sam Smiths and JD Wetherspoon offer excellent value for money when compared with the average pub on the High Street.
Drink the cheaper brands: Common brands such as Fosters, Carlsberg etc are likely to be far cheaper than your premium brands, prices can vary as much as a £1 in some bars. So with spirits, wines and beers stick to the cheaper brands.
Don't get sucked into the generosity of the typical English Round: It is an English tradition that when you go to buy a drink you ask those around you if they would like a drink. This is fine if it is 1-2 people but it can mount up to being far more people and you are unlikely to get those drinks back. Decline drinks from those in big rounds and stick to being in a small drinking round.
Take advantage of happy hours: Lots of bars (particularly cocktail lounges) have happy hours to entice you in. Take advantage of these offers but dont be sucked into paying higher prices when the happy hour finishes.
Only spend the cash that you are happy to in your wallet: As you get drunk it is easy to get carried away so take the set amount of cash you are happy to spend and only spend that. Once you starting using your card you can lose control.
When dining out look for BYO venues: London has some good Bring your own alcohol venues where you will only have to pay a small corkage fee. these can reduce your final bill significantly.
Look on pubs websites for deals: Some pubs offer a free drink for new customers so check the website before you head to the bar you are going to you. You may score your first drink for free.
Catch public transport home: Catch public transport home as cabs can be expensive. The London night bus service is excellent, research your trip home before you head out.
Bottomless Brunches: Keep a look out for bottomless brunch offerings where your drink won't hit the bottom.