With your budget You will most likely have to go for an AMD CPU , as a decent Intel will not leave you much for the rest of the build . I have to say that with a budget of £800 to include peripherals you are not going to get very good performance . My advice would be to save for a little longer and aim for £1000 . The extra £200 would go a long way towards a decent screen , keyboard / mouse .
Surface Pro 4 UK release date, price and specs: Thinner, lighter, faster with new Type Cover and Pen