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

Here is Why You Need An Adapter

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

Eritrea

In Eritrea, outlets of type C and L are in use.

Type C

Type L

Great Britain

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

Type G