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

Here is Why You Need An Adapter

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

England

In England, outlets of type G are in use.

Type G

French Guiana

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

Type C

Type D

Type E