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

Dominica

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

Type D

Type G

United Kingdom (UK)

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

Type G