You Do Need power plug adapter while traveling from Bhutan 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 Bhutan are C, D and G. This is how they look like.

Bhutan

In Bhutan, outlets of type C, D and G are in use.

Type C

Type D

Type G

United Kingdom (UK)

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

Type G