I usually refer to the U.S. CDC travel advisory page: http://www.cdc.gov/travel/. I would guess the U.K. has something similar.

There is no malaria risk in the areas you list. However, there is Dengue, another serious mosquito-born illness. So preventing bites is still important.

It is important to talk with a doctor, if you haven't already done so, because there are other vaccinations that are recommended before travel to many areas in Southeast Asia.

Have a great trip!