FOR most military personnel, life in Civvy Street can be a daunting prospect. But for one non-commissioned officer with the Royal Navy, it is not so much a question of how to survive after he retires when his tour of duty in Hong Kong ends in 1996, but more how to spend a recently-won fortune. In fact, Chief Petty Officer Rohan Mitchell's main concern after scooping a GBP2.26 million (HK$27 million) jackpot in Britain's biggest pools win was whether he would be allowed to remain in the armed forces. ''Will the Navy let me stay on?'' he asked after he claimed the prize. ''The Navy has been my life. I have 18 months left to do out of 22 years' service and I would love to complete it.'' Mr Mitchell, 38, from Rickmansworth, Hertfordshire, will arrive in Hong Kong on Tuesday and take up a desk job at HMS Tamar on Stonecutters Island. ''Obviously, everyone is delighted for him,'' said a military spokesman. ''But he is not going to be given any special treatment.'' But the veteran of the Falklands War will be ''protected'' by the military from any unwelcome publicity and people more interested in his money than his welfare. ''We will protect him, but he will receive nothing more than we would do for anyone else,'' the spokesman said. ''But it can't be bad with GBP2.2 million if you're 38 and single.'' Mr Mitchell, who is spending this weekend on holiday in Britain since leaving his last posting, will be quartered in ''single men's accommodation'', although he is likely to be allowed to live outside the barracks if he wishes. He was presented with a cheque for GBP2.26 million, which he won with a GBP1.80 stake, on board the warship HMS Belfast on the Thames River.