Worth checking with a legal man but, if you are paid on a monthly basis then I believe that you are only required, in law, to give one months notice. That said, don't get yourself a bad name in avaition, it is too small. If your new and prospective employer is insisting you break your existing contract then I would not trust him.
You have 'shown your hand' to your present employer so you are now 'stuffed', if you are worth having then your new employer will just have to wait.
(P.S. Laker had a six month notice clause, no one ever worked it and none were taken to court).