Amazon is routinely 25-40% cheaper than most UK high-street bookshops (such as there are anymore). If you find a cheap deal on Amazon.co.uk, chances are you won't find it in any shop - though there are of course limited exceptions to this rule.

It should be noted that with the demise of Borders and Books Etc. in the UK, there are very few large bookshop chains left. The only major one is Waterstones (and it's not looking too good for them, either...). In London, you've got a few branches of Foyle's and a few Blackwells, but there aren't many of either and neither is known for its low prices.

I hate to say it (because Amazon will eventually kill all high-street bookshops) but if you're looking to save money, it's probably your best bet.

Just make sure that the hotel knows you're coming so that it doesn't send the package back. Get written confirmation if you can.