Once again using the example figures I used in my previous post....
Given that you don't pay NI on a pension, then a pension of £35,000 actually represents the take home pay of a salary of £39,800 (lets call it £40k to make life easy).
Therefore, a 55 year old retiree on a £35,000 pension would only need to find a job paying £30,000 to have the same take home pay as they would if they rejoined as FTRS on £70,000.
This might not be possible, or they might not want to work that hard, but even a part time or low paid job pulling in £15-20k would mean very little drop in life style. Indeed, as I said before, given the upper tax band effect and not paying NI, doing nothing and retiring permanently would result in a drop in take home pay of nearer a third than a half.
In summary, I think it highly unlikely that many 55 year olds will consider rejoining as FTRS. It simply doesn't make sense, there is very little financial incentive.
I did know an ex Wg Cdr and ex Gp Capt who rejoined as FTRS Flt Lts. They were both younger than 55, one considerably so. Here the numbers would be very different, and I'm sure it made financial sense. However, one of the biggest draws for both of them was that they returned to flying and Sqn life.
The FTRS Sqn uncle posts under discussion are non flying posts.