Anti roll bar bracket broken - Why?

Don't remove it, The sway bar is there for a Good reason.
Simply take the Defender back to whoever fitted the airbags an get them to do the job properly and for NO charge, After all they ****ed up the job that caused this issue. [thumbsupbig][thumbsupbig]

The person fitting the air bags has dropped the axle too far, inverted the antiroll bar links, and THAT is what has broken the bracket. I would be having a chat to them.