You Do Need power plug adapter while traveling from French Guiana to Great Britain.

Here is Why You Need An Adapter

The outlet and plug type used in Great Britain is G and in French Guiana are C, D and E. This is how they look like.

French Guiana

In French Guiana, outlets of type C, D and E are in use.

Type C

Type D

Type E

Great Britain

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

Type G