Ben,
She was a launch tug (not a tanker) blt at Clelands, Wallsend in 1949 for Burmah Oil, passing over to Everard ownership in 1957. (she was one of 3 they took on, Spinnaker ex BOC 39, Spanker ex BOC 40 and Stalker ex BOC 41)
Think she was originally used in Great Yarmouth area, before being moved to the Thames - though could be getting confused with one of the fleetmates
There is a good picture of her in Ken Garrett's Everard of Greenhithe (published by WSS in 1991)
Krispen