A Bolkow BO 105 helicopter was used in the operation.
G-BATC was noted in the movements for RAF Valley late June 1981 by the MAS in 'Flypast', but with no notes.
Trinity House did/do use Valley when operating around the North Wales coastline, do 2 + 2 add upto 5 and provide a specific period within 1981? Confirms Bolkow BO 105 was around though.
Thanks Steve and Brian for Merseyside Aviation Society notes.