I feel that the fact my beret still fits (and over the same amount of hair) is evidence that I've kept in shape although as you point out uniforms have a built in shrink factor.
From The History of The 4th and 7th Royal Tank Regiments website:
August 1978
The Regimental log “Chinese Eye” records that this was a difficult time. The Regiment was sixty under strength – almost a squadron – and tank skills had suffered from the two Op Banner tours in quick succession. There was great pressure on all ranks and sport inevitably suffered.
One piece of good news for the officers was that the ceremonial astrakhan beret was finally given the heave – officially!
http://www.4and7royaltankregiment.com