You Do Need power plug adapter while traveling from Montserrat 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 Montserrat are A and B. This is how they look like.

Montserrat

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

Type A

Type B

United Kingdom (UK)

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

Type G