You Do Need power plug adapter while traveling from Vatican City to Great Britain.

Here is Why You Need An Adapter

The outlet and plug type used in Great Britain is G and in Vatican City are C, F and L. This is how they look like.

Vatican City

In Vatican City, outlets of type C, F and L are in use.

Type C

Type F

Type L

Great Britain

In Great Britain, outlets of type G are in use.

Type G