Indeed it was. Replaced by the Mexicana Comet but whilst a wonderful aircraft, it lacked props!
Both these aircraft had a common cause, that when BOAC was retiring their fleet they got leased out long term, the Argonaut to East African, the Comet to Mexicana, and for both BOAC somewhat unwelcomely got them back long after the fleet had gone and the secondhand market for their type had passed them by, so ended up being used for whatever training was still relevant on them.
The book "BOAC an Illustrated History" has a cleverly selected cover photo of a Comet, 707 and 747 together, all in BOAC livery. Theoretically impossible as the Comet was retired long before the 747 came along, it is staged with the Comet trainer, back in full BOAC livery, parked among these other types. The Argonaut was still around Heathrow then I believe, shame it couldn't have been cosmetically tarted up to join the others :