Can British Trident submarines launch from alongside?

Can British Trident submarines launch their missiles from alongside a pier?

This capability is described as neither confirmed nor denied for the latest variants.

The ability of current Trident variants to launch from alongside is left unconfirmed. The question arises during an argument that submarines remaining in port might respond after an attack on the boat already at sea. Pier-side launch therefore remains an uncertain part of the deterrence argument.