There is a bit more to it than that, basically it has a lot to do with SERPS, most people in the military contributed to the pension scheme whilst serving, then along came SERPS and 99.99% opted out, no longer contributing to the pension.
The MOD continued to pay towards your pension, along with NI contribution's, basically there was a massive C**K up, the HRMC want the money back, so they along with the MOD have started to claw it back.
It however does not effect everyone, some are more unlucky than others, as they say luck of the draw, depends on your paymaster at the time.
In January I started drawing my state pension, it has affected my Army pension, I have a state pension and a Army pension which is more than my personal allowance, to pay that that tax they are deducting it from from my Army pension so I am getting a reduced amount.
I have posted another link that might help explain it.
https://www.gov.uk/government/publicati ... dification