Prices of laptops have dropped a lot lately so there are many available for £300 and upwards.
The latest Intel CPUs are called i3 (and i5 and i7) and an i3 shoud be fine for you so see if you can get one with an i3 CPU on it.
Many new computers come with Office 2010 Starter on it which consists of Word and Excel with slightly limited function. This is NOT time limited and will run forever so this may be good enough for your work.
However it does not include Outlook so if you really need it you may need to buy it (there may be way of you not needing Outlook itself but getting your mail some other way like Windows Live Mail which is free) or via a web interface.
To be honest there are hundreds of possible laptops you could buy, and they are sold through many supermarkets (Tesco etc) as well as Comet, PC World, Dell etc etc, so it is difficult to suggest just one.
I use a web site called HotUkDeals where members of the public post good deals and it may be worth looking on there to see when a good laptop deal is posted (then get in quick before they all go).
Note that people can "comment" on the deals so read the comments and see if people really do think it is a good deal.
See web site here
http://www.hotukdeals.com/computers/all/new