Note - Accessing the pension fund at 50 doesn't mean retiring, you just need to have left the employer where it was earned. At least for DC occupational pension schemes..
You can build a pension pot which grows tax free and which can be accessed at 50 with a tax free lump sum of 25%. Using the lump sum to pay off the mortgage and move the remaining 75% to an ARF where it will continue to grow and you don't need to start drawing on this until age 61. You are then free to move to a new job either at the same level - or as I plan to do, at a much lower level as I take the foot of the gas and find a more relaxing job.
I feel this is a far more flexible than paying down the mortgage as I will be unable to leverage this money later if plans change and inflation/wage increases over the past 15 years have made my mortgage manageable
50+o