The Royal Observer Corps.

Contrary to popular belief, the Filter room was not handed to the Royal Observer Corp (ROC) (reported as September 1944) Instead; the ROC had a purpose built, above ground facility built in January 1940 (ROC code number 30/D2. Map Ref Z220676) In 1959 it was moved beside the public house (The Crofters Lodge) at map ref *****. The confusion between the ROC using the Filter room stems from the fact that the ROC built themselves an underground facility behind the public house. It remained in use until 1968.
This is a report which the ROC conducted in 2000 on their bunker post. In use February 1962 - October 1968. OS Grid Reference: NZ21496748. Location On the north side of Crofters Lodge Pub, east of the telephone exchange "When visited in 2000 the post was still extant on a low mound in the North West corner. The post was amongst low trees. All surface features were intact including the ventilation louvers. There was an iron bar across the hatch securing it. Internally the post was clean and dry. The table, shelf and cupboard remained in place together with a GPO junction box, some papers, some wiring and a large home made cardboard dial. The whole government site (excluding the Group Fighter HQ) has now been cleared for housing and the ROC post is scheduled for demolishing in October 2004."
The Kenton Bar site was placed on the surplus list in 1947 and the land surrounding the operations room was used for offices by the Ministry of Agriculture with a number of single storey brick buildings being constructed for the purpose. Many of the above ground buildings associated with the Group Headquarters were demolished at this time. In 1950 the Kenton Operations Room was proposed as a Sector Operations Centre for the Northern Sector in the Rotor scheme * but discarded in favour of purpose built one near York.

* Rotor scheme
The UK radar system was rapidly run down towards the end of the Second World War. It was then envisaged that it would be at least another ten years before another major conflict, but the first Soviet nuclear test in 1949, and the outbreak of the Korean War one year later, dramatically changed that view. The then perceived threat was on onslaught of Soviet Tu-4 bombers (exact copies of US B-29 Superfortress, obtained when four crash-landed in 1945 in Siberia after a bombing raid on Japan) armed with 20 kT yield atomic bombs. It was doubtful that with the decayed state of the UK's air defences that they could have been detected and intercepted. With great haste, the Cherry report of 1949 recommended an urgent overhaul and improvement of the UK's air defences, under the codename Rotor. Due to this, it was recommended that the sprawling network of some 170 radar sites left over from the last war be rationalised and consolidated to 66 sites, and that the best existing radar be completely re-built to higher peacetime standards. The essential elements of the wartime Control and Reporting structure were maintained - a hierarchical command and control system, separate sectors etc. The Rotor project was divided into two areas, east coast and west coast, partly as an economy measure. The threat was seen as higher on the east coast, so the majority of the sites had underground protected operations rooms. The west coast had mainly surface bunkers or semi-sunk ones.