You Do Need power plug adapter while traveling from Wales to Montserrat.

Here is Why You Need An Adapter

The outlet and plug type used in Montserrat are A and B and in Wales is G. This is how they look like.

Wales

In Wales, outlets of type G are in use.

Type G

Montserrat

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

Type A

Type B