I took this photo at Biggin Hill during the 1954 Royal Observer Corps "Recognition Day". It shows RAF Neptune MR1 WX547 from the Fighter Command Vanguard Flight (1453 Flight) based at Topcliffe in Yorkshire.
Vanguard Flight Neptunes carried out some of the initial Airborne Early Warning Radar trials over the North Sea, but according to Google they were not a success (see quote below).
By the 1950's, the Royal Navy and RAF had started the development of AEW systems. The Royal Navy ordered the development of an AEW Fairey Gannet, whilst using the AN/APS 20 radar equipped Douglas Skyraider from the US as a stopgap, and the RAF set up the "Vanguard Flight", also known as 1453 Flight, equipped with Lockheed P2V-5 Neptune's. They were not a success, and the flight was disbanded after 3 years. Therefore, the only operational AEW systems in use by the British armed forces up until 1970 were operated by the Royal Navy.