Key stuck

I have a 2010 mini Cooper diesel and the battery went flat after bein stood in the garage for 7 months. I put jump leads on and it started straight up, I left it running 30 mins and pressed stop button to turn engine off n lock car up till I can get it to mot station. When I pressed stop button the engine turned off but key won't release, thinking the battery isn't holding charge to release the key I again tried jump starting the car but this time nothing, no lights n boot locked n car would not start, any ideas please???