You Do Need power plug adapter while traveling from Belize to United Kingdom (UK).

Here is Why You Need An Adapter

The outlet and plug type used in United Kingdom (UK) is G and in Belize are A, B and G. This is how they look like.

Belize

In Belize, outlets of type A, B and G are in use.

Type A

Type B

Type G

United Kingdom (UK)

In United Kingdom (UK), outlets of type G are in use.

Type G