The Mark 5 electrical starter trolley was used to provide power to smaller aircraft from the 1960s to the mid 1990s. They were commonly seen with Wessex and Canberra PR9 but I have seen them plugged into Shackleton Mk2 and AEW2. They were initially painted RAF blue/grey, sometimes with a yellow roof, during the early 70s they were yellow and eventually toned down to green.
This trolley is with A Flt / 22 Squadron, RAF Chivenor. 1992.
The Royal Navy also used the Mk 5, here it is seen providing power to a Sea Devon at Culdrose, 1989.