55 mins is more than enough.

T2A and T2B are one terminal (think an L shaped corridor) separated only by passport control.

So on arrival you go to transfers, through security, and up into the main terminal. It all takes seconds.

The only issue is that the MA desk have proven themselves useless at issuing BPs on anyone except MA (even it's an MA codeshares), so don't be surprised if they send you to the gate for checking in.

It doesn't take more than 5 minutes to get from one end of the terminal through passport control to the other end.