what are your other 3 choices? this would help us a lot.
To my knowledge the only schools that take grads with law are:
Kings, Keele, Newcastle, Nottingham, St Georges, Southampton and Swansea.
Really you would be better suited to a 5 year course. You will struggle no-end on a 4 year and although you may relish the challenge and you may be quite capable of doing it, I would impress upon you from my own experiences just how difficult it will be.
I would go for 2 four year and 2 five year courses and get your 4th choice for a 5 year that doesnt use the GAMSAT.