You Do Need power plug adapter while traveling from Liechtenstein to United Kingdom (UK).

Here is Why You Need An Adapter

The outlet and plug type used in United Kingdom (UK) is G and in Liechtenstein are C and J. This is how they look like.

Liechtenstein

In Liechtenstein, outlets of type C and J are in use.

Type C

Type J

United Kingdom (UK)

In United Kingdom (UK), outlets of type G are in use.

Type G