Plessey Solent Gas Turbine Jet Engine in serviceable condition. These engines were designed in the 1960's and were fitted as part of the starting system in the Phantom F4 aircraft Spey engine. There is quite a lot of information on the internet on removing the free power turbine and converting these units to provide thrust power.
This particular unit has it's original records and is extremely rare being with its 731 "Serviceable Condition" paperwork.