Don't buy Acer! I bought 10 for our staff and they lasted less than 12 months. Warranty support is a waste of time - laptops came back in a worse state of repair than when they went. Got over 150 HPs in use and they don't give me any aggro. A few Dells as well which are ok but not as tough as HP.
HP have some cheap deals at the moment - some cashback offers too. HP have recently had some problems with the power management on their mainboards but they swapped them all out no problem.
Dell are also ok but you have to make sure that the case screws stay tight - they have a habit of undoing after a year or so.
You really do get what you pay for with laptops <£700 so spend as much as you can afford. Over > £800 a bit of paying for the name comes into it too.
www.misco.co.uk are ok to get an idea of pricing/models but if you're buying HP it doesn't matter where you get it from because of the Global warranty supplied by them.
www.hotukdeals.com is an awesome site for bargains/vouchers/codes etc and they quiet often have Dell deals listed.
...and if you deal with Dell direct make sure you haggle on the phone for free delivery, bag, mouse, web cam etc. they will ALWAYS give you something. If they won't hang up & ring back to get a different rep. If you want to knwo if I price on Dell/HP is any good PM me the spec and I'll let you know. We have a Platinum agreement with Dell & internal HP account manager so I'll be able to let you know how much more haggling to do!