So my experience was this: I left the UK in 1998 and hadn’t given the UK pension a second thought until March this year when I was having a chat with an AI about my partner’s UK private pension and moving that to Australia. One thing led to another, and the AI advised that we might both be eligible for the UK state pension. I filled in my CF83 form in mid-March this year, and got a reply in late May (dated late April) saying I was eligible to back pay 20 years of class 2 contributions (£3.3k), which takes me to 26 years of NICs. I was given an 18-digit reference number which I used to make the payment a few days before the 31-day deadline (using a Wise UK account and the Faster Payment system).
And today I received a letter (with the same late-April date as the earlier letter) inviting me to pay the last 6 years at class 2 rates! (Which I’ve already paid, as part of the 2006-2026 payment.)
So I guess I’ll just wait and see what happens. I’m assuming it’ll all go ok, and that I can pay 9 years of class 3 NICs going forward to take me up to 35 years,
Given my experience, I don’t really understand what that 5 April 2025 deadline was all about.