I can't speak about the UK, but even looking at the Spanish version, the i5s are identical in price for the SP3 and SP4.I've been advised to steer clear of the core m3 model...
Using a student discount MS has the i5 4gb for £764.10 + keyboard (£98.99)
Other than ebay etc, is this the cheapest it's going be for some time? Debating waiting until January sales for example. Thanks