You Do Need power plug adapter while traveling from Balearic Islands to Great Britain.

Here is Why You Need An Adapter

The outlet and plug type used in Great Britain is G and in Balearic Islands are C and F. This is how they look like.

Balearic Islands

In Balearic Islands, outlets of type C and F are in use.

Type C

Type F

Great Britain

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

Type G