Specifically, to answer the question above, it appears that in some cases a service trail can be dispensed with:
Dispensing with Service proceedings
34. Whilst desertion remains a serious offence there are circumstances in which it would be of no benefit to try someone for this offence see Chapter 18 (Terms and conditions of enlistment and service). The main provisions are outlined at paragraphs 35 to 37 below.
35. Confession of desertion. If a Service person makes a confession of desertion37, the CO may decide, with or without the consent of the Director of Service Prosecutions, to dispense with Service proceedings, having taken into account the circumstances of the case and of the person who made the confession38.
36. Forfeiture of service following confession of desertion. If a Service person makes a confession of desertion and the CO decides to dispense with Service proceedings, service is forfeited according to the following rules:
a. The date of enlistment will be deemed to have been the date which precedes the date of the CO’s decision by the period of service that has not been forfeited.
b. The Service person who confessed will be liable to serve for an additional period equal to the period admitted as desertion.
c. The date of entitlement to discharge from the regular forces, to end service with the regular forces or to be transferred to a reserve force, will be postponed by an equal period.
d. The CO may decide that the person who confessed is not required to serve for an additional period under sub-paragraph 36.b above39.
I knew of a couple of lads that went AWOL ,one handed himself after a year as he had run out money and lost his job,couple of months in DQs and out and the other was caught after about six months,again outside via DQs for a couple of months
We had a bloke, Bill, brought into Viccy Barracks Recess in 1963. He'd gone AWOL around 1946. We kept him for about two weeks. Not much to do beyond give him the old heave ho. But recent AWOLs just might do DQs and out or DQs and stay in, having to make up the time. At the end of the day, better to give yerself up or you'll be looking over your shoulder forever. They don't forget.