The Guardian has put together a great list of the 10 Best Guided Walks in London.
Here’s an excerpt:
Fancy a trip down Diagon Alley, a view of an elusive Banksy or a look at the spot where William ‘Braveheart’ Wallace was executed? Here are 10 top London guided tours.
London is best seen on foot. But in a city so historically, culturally and geographically vast, you might need a guide. Fortunately, a burgeoning community of tour operators is ready and waiting to lead you through the streets of London. Ten of the many options – including the mainstream and the more offbeat – are suggested below. Check the websites for full details, as most walks require pre-booking.
If your like me and are completely broke, you can find some great free guided walks on this site http://www.whatsfreeinlondon.co.uk/free_guided_walks_in_london.html