Your pension savings may already be protected
As mentioned, the lifetime allowance was introduced in 2006 and was reduced in 2012, 2014 and again more recently in 2016.
Each time the lifetime allowance reduced, if you had already planned your pension savings on the basis of the higher lifetime allowance you could protect your pension savings by applying to HMRC.
If you have applied for a previous protection i.e. enhanced protection, primary protection, fixed protection 2012, individual protection 2014 or fixed protection 2014 you should have received a certificate to confirm your protection.
However you may still be subject to the lifetime allowance charge if you lose this protection. You can find more information these protections and when they may be lost here.