The MPAA is a reduced annual allowance for contributions into a money purchase scheme. It is triggered when individuals flexibly access their money purchase pension in certain ways. Once the MPAA is triggered carry forward is no longer available in relation to contributions to money purchase schemes.
The MPAA is currently £10,000 and applies from the moment it is triggered. So, it is possible to pay in more than £10,000 for the tax year in which the MPAA is triggered if the amount paid in afterwards is no more that £10,000 and the total amount before and after the trigger does not exceed the standard annual allowance and carry forward available. Any amount exceeding this will cause an annual allowance charge.
The MPAA does not affect how much can be paid into a defined benefit schemes and there are special rules about what a trigger is for hybrid schemes.