Try inserting the key slightly less than all the way in (mm or so), and keep trying different positions, but don't use force to try and turn the key, this will make matters worse. It will turn if you persist.
When you get the barrel out you'll see why I suggested this; it only takes a tiny fraction of lengthways misalignment of the key in the barrel to cause the tumblers to not sit flush. What happened to ours was that 'the internet' recommended bashing the end of the key, and this really didn't help, it just bent something such that the key could go in too far. If you've done any significant bashing of your own, the same thing may have happened.
If you try for ages and still can't get it to turn, there is another way...
Right-angled screwdriver to get at the cowling screws behind the wheel, remove cowling. Hammer/chisel to undo the two fixings on the top that hold the steering lock, then you can drop the whole assembly off. Then you can start it with a screwdriver in the switch. Some possibility of airbag deployment while bashing... AA man said he'd done a few and never got hit though.