For Meg. My top five tips for living frugally in London (such as they are):
1. I think you've beaten me to it on this one, but taking your own lunch to work (and not being tempted to buy out) is a massive money-saver. Hopefully you getting free lunches will help you out a lot.
2. Samuel Smiths pubs will do you a cheaper (house brew, but decent) pint than most other pubs in London, and happily they're all over the place.
3. I don't know where your job will be in relation to your house, but if you have to fork out for a monthly travelcard (which will hurt) then make the most of it -- you can make it well worth the cash if you let it take you to all the freebie cool places in London. Use it everywhere, and if you're not on your own (or very brave) get night buses home rather than taxis.
4. Supermarkets. Dull, but true -- don't get sucked in by the allure and convenience of the train station mini-supermarket if you can at all help it. (We're all trendy young things who just dash in to buy some wine and fresh pasta for dinner on the way home... OR SO THEY'D HAVE US BELIEVE.) They'll have added 15% onto the cost of everything. Asda is by far the cheapest place (sadly few and far between) but isn't so great for fresh foods. Waitrose and Sainsburys are the most expensive. Tesco is an OK mid-range option. (god this is boring, sorry!)
5. Free things to see and do! So many free things and I don't make nearly enough of them all. My favourite London place of anywhere is the South Bank, which has the National Film Theatre, street performers, free music, the Tate Modern and fabulous London views, all just for starters. All the museums are free and well worth a visit. In fact, having just tried it, typing 'free things to do in London' into Google gives you 77,300,000 results...
I hope these help -- good luck!
Also, 6., don't have an expensive yarn habit. Ha.