Best I can find is https://www.gov.uk/how-to-vote/voting-by-proxy
You can ask anyone to act as your proxy - as long as they:
are registered to vote
are allowed to vote in the type of election taking place
can vote in the polling station stated on your poll card
They’ll need to take their own photo ID with them to vote in some elections.
If they cannot get to your polling station, they will need to contact your local Electoral Registration Office to arrange to cast their proxy vote by post.
My interpretation is that it sounds like a yes.