My source was "Convoy ! Drama In Artic Waters" by Paul Kemp.
He states "JW.64 sailed from the Clyde (the Loch Ewe anchorage having been closed down) on 3 Feb 45.
AFAIK Loch Ewe was in continuous use after the mauling sustained
by OA.178 on 4 July 40 off Portland, and the decision to route these convoys round northern Scotland to the N. Minch via Loch Ewe.