Ananda
The Bunker Group
I believe, the British only used light Tanks, due they did not expect any armoured opposition during Malayan emergency time. However NICA (Netherland Indies Collonial Army) did operated M-4 Sherman (which basically already in Medium-MBT catagory), if I'm not mistaken on the worries that the Indonesian Revolutionary forces able to bring live some of ex Japanese Tanks. In short Nica bring Sherman in the anticipations of possible armoured plus Anti-Tank oppositions.In Vietnam, the Australians and Americans operated their MBTs, in very thick jungle, to support their troops. The NVA however, when it came to combat, tended to deploy their MBTs in more open spaces, like the coastal roads, during the advance to the South in 1975 and the Easter Offensive in 1972. The use of armour in a thick jungle setting was mostly restricted to the PT-76 - now I could be wrong here but I'm not aware of the NVA using its MBTs for combat in thick jungle [not saying they couldn't], like the Australians and Americans did. The British also used Comet light tanks in Malaya during the Emergency. As OPSSG said, a lot depends on having the proper engineering assets in place to support your armour.
Now the Indonesian revolutioners did not able (as far as I know) managed to bring ex Japanese Tanks to operations. However they managed to operated and fielded some Japanese Anti-Tanks assets. Thus, when an Army expect armoured confrontations or credible anti-tank oppositions, they will bring heavier armoured even in the Tropical jungle conditions.
Like I said, the lack of MBT to MBT clash in the Vietnam not because MBT can't operated in Vietnam, however because NVA decided not to bring their T-55 head on often enough with US M-48/M-60. Still the record due show (at least what I've been read on few publications), that US M-48/M-60 did have some engagement with NVA T-55. Although not in large scale.
On the lighter side, some retired generals turn politicians that oppose TNI effort to introduce MBT/Leo 2 now, when they're still in active duty on the 90's did tried to bring Leo 1 to TNI inventory. Just like I said on my past posting, the deal boggled down due to Soeharto Children got better deal for Scorpions.
Just to show, the arguments on MBT sometimes already clouded by political considerations. The conditions of Kalimantan/Borneo is not much different than Indochina now, and yet Cambodian and Vietnam do manage to operated their MBT quite effectively.