You need to ask yourself why you might actually need a touchscreen computer. If you'll be doing any significant amount of typing (e.g. producing Word documents) you might find a conventional keyboard better suited to your needs. I suggest a policy of 'try before you buy' might be best, as with this model from PC World (or from Currys - they're the same firm anyway):
http://www.pcworld.co.uk/gbuk/samsung-series-5-dp500a2d-21-5-touchscreen-all-in-one-pc-17392876-pdt.html
Reviews here:
http://mark.reevoo.com/reevoomark/en-GB/product?product_group_id=10783915&retailer=REF
Remember that touchscreens add considerably to the price of a computer. A similar specification for a standard desktop would be considerably cheaper.
Irrespective of whether or not you go for a touchscreen model, it will be hard for anyone here to make specific recommendations unless you tell us what you plan to use the computer for. If it's for gaming or video-editing you'll need a really fast processor, but paying for such a high-spec processor would be a total waste of money if you only plan to type documents, view images, and browse the web. (In that case you might as well save yourself several hundred pounds by buying a basic refurbished desktop for around £100, plus a decent monitor).
Chris