The Minolta XD7 is a nice small light SLR which can be used fully manual, though it does have shutter priority and aperture priority when used with the right lenses. You could probably get one on ebay with a standard 50mm for between Ł50 and Ł75, which would leave plenty of money for film! It gives full viewfinder information too which is essential in manual mode. You're probably best avoiding lower end SLRs as they can be a pain to use manually, and some often don't offer full manual control.