Imagine my surprise when I looked at the back to find that it was used with a GB stamp. There was no date to the message. Interestingly, it is marked at the top with the word "Forces". Looking at the poor postmark carefully, I can make out the letter (FIEL)D followed by a P(OST) after a gap. It would correspond to a Cave type 3 FPO postmark. The date is also unclear. At the bottom, one can perhaps with a bit imagination make do with the number 1061. FPO 1061 was based in Simangang, Sarawak as well as Brunei where it was used by the 40 Commando squadron of the Royal Marines.
The message appears to be one from father to son. Neil was probably on a training exercise in Sabah. At the end of which he had some time for some R&R (rest and recreation) in Jesselton. The card was bought in Jesselton but posted back at the base.
Brititish Field Post Offices in Sabah:
BFPO 660 Labuan 1964-68
BFPO 663 Tawau 1964-66
BFPO 670 Jesselton 1965-67
Field Post Offices in Sabah:
FPO 154 Jesselton 1965
FPO 166 Labuan 1964-65
FPO 169 Tawau 1964
FPO 450 Tawau 1965-66
FPO 573 Labuan 1963-64
FPO 766 Labuan 1965-68
FPO 1030 Tawau 1964
FPO 1035 Kota Belud , Jesselton 1966
Besides the British, there were also various Australian Field Post Offices.
Ref: Sarawak Journal vol 49 p 93-95
This cover has a very nice strike of a Cave type 1 cancellation of FPO 51 based at Brunei. There is an index c above the date. FPO 51 was one of the FPOs allocated to BFPO 605 in Brunei. It is also interesting that the sender's address also referred to the Royal Brunei Malay Regiment where the British troops were housed.