Preserved pensions may now be paid early, subject to consideration by the Service Personnel and Veterans Agency (SPVA) if a veteran has become permanently unable to work full-time, in any capacity, through ill-health, and this condition will continue until preserved pension age. Early payment of the pension may be subject to review and stopped if it is considered that the criterion for payment was no longer met.
For more information on preserved pensions visit www.veteransuk.info. To find out if you are entitled to a pension, call the JPAC Enquiry Service on 0141 224 3600
In general, you can't. Unlike a personal pension which is portable and has a cash value that varies with the value of the fund in which it is invested, the military pension does not have a value.
Now, this all "AFAIK" and for the 1975 version. If you have completed 10 years of service and have left, you will have frozen your pension until you are 65. If you are not married, I am certain that the pension dies with you, should you croak before you are 65. If you are married, your missus collects 50% until she croaks or remarries. If you are dying now, you might be able to release the pension but not the cash.
If you are still serving, and decide that you would prefer a personal pension, I would tell you to lie down in a darkened room and wait for the feeling to go away. But, you could then take it away, and perform financial wizardry on it and turn it into a much smaller pot of cash. However, most of that would exploit loopholes or be against HMRC rules!