I had about 23 years of pension contributions in the UK through NI (National Insurance) before I came to Indonesia. I continued the contributions voluntarily, which was not very expensive, and became entitled eventually to a full peinsion. I deferred the pension for almost 10 years and now get almost a double pension (over £1,300 per month). This does not rise annually because I am non-resident, but it is also not taxed.You can only go back 6 years I think in terms of paying to catch up. So let's say you had 7 years from when you were in the UK (it should be on your national insurance record), pay back 6 years as a lumpsum, and pay for the next 15 years (assuming you are 52) you will achieve 28 years, entitling you to 28\35 of the full pension at age 67.
All details are on gov.uk.
Of course if you are not planning to live past 67 then there isn't much point!