Read the thread April 2011
Eventuate (eventuate.org) are a great company and they are so creative. They do a lot of work in London for some big names and have worked for me many times (at big corporate company, Financial Services). They are based outside London so their prices are good. They do quite a lot of parties so get a chance to be really creative so I am sure they will have lots of ideas for you.
The food at the the-recipe.co.uk is also very good and David is so passionate about what they do.
Hope that helps. More