Agree with you Dave - this is HMS "Deer Sound". Built for Port Line by J.L.Thompson, Sunderland and requisitioned before completion in 1939 and fitted out as the minelayer HMS "Port Quebec". Went to John Brown's, Clydebank in 1943 for conversion to an aircraft maintenance repair ship, being commissioned in January 1945 as HMS "Deer Sound" until 1947. She was delivered to Port Line in December 1947 as "Port Quebec" following conversion to a merchant ship by Swan, Hunter & Wigham Richardson, Newcastle. Broken up, as "Port Quebec", at Keelung December 1968.
Port Quebec in the gallery http://shipsnostalgia.com/gallery/showphoto.php?photo=11128
I would say, the unknown ship is possibly a different - but almost similar looking ship - converted for WW II purposes.
The Flag L superior together with the landing craft indicate a role which is neither Minelayer nor Maintenance.
The lower numeral is not 9 which has white uppermost to the hoist.
Most wartime Ls seem to have been destroyers. This has to be a Landing Ship Infantry. The naming seems premature.