For anyone who might be interested I now have the answer to this. I emailed the Bovington Tank museum and they were very helpful and were able to answer the question.
Here is the reponse:
Re: Markings
The black cat on a yellow square represents British Land Forces Borneo.
The circle would represent C Squadron ( Squadron HQ was a diamond, A Sqn. a triangle, B Sqn a square, C Sqn. a circle). Given that it’s a black and white photograph it’s difficult to ascertain whether the circle is yellow or white (it’s most likely yellow). The British Army registration number is definitely white though. The officer’s `tent’ hat identifies the unit as 8th Queen’s Royal Irish Hussars who were out in Borneo during 1964.
The white number 31 on a red/yellow square is the serial unit number and most likely corresponds to them being the Armoured Car Regiment in Burma. Unfortunately, whilst identify World War Two serial numbers is relatively straight forward there is little information on markings for post-war British units.