unconditional offer

Hello, I passed my French baccalaureate in 2014 and have been at french university for the past year, but i quickly realized that i wasnt enjoying it so decided to apply to univeristy in england, after receiving an unconditional offer from portsmouth i accepted it thus refusing the other offers, but they now have sent me a message asking for my university results(which are not good because it was not for me) saying "on receipt of the transcript, the Tutor will be able to make a judgement on your overall performance and suitability for the course" which has now got me worried. Are the allowed to go back on an unconditional offer ? Or am i just missunderstanding this as them just wanting it to finish my application ?

Don't panic. Perhaps they want to see your grade transcripts as evidence that you studied at that university? regardless I would contact them email/phone just to clarify everything Don't worry