According to my late father's log books, he made at least six flights in the Bobsleigh (from the prone position, including spinning) between July and September 1951, during his time as a test pilot at Aero Flight, RAE Farnborough.
Perhaps the following extract from his memoirs might be of some interest:-
Later in the year we had another interesting project. For some time there had been thoughts about how to help fighter pilots withstand the high G forces imposed during manoeuvres and it was realised that if they could be lying down rather than in a sitting position they could be subjected to much higher G forces before blacking out. It was therefore decided to investigate the practicalities of piloting an aircraft from a prone position, and a twin engined aircraft the Reid and Sigrist Desford was modified to incorporate a prone piloting position in the nose retaining the normal cockpit with dual controls in the centre fuselage. The special cockpit in the nose accommodated a pilot lying face down on a padded ramp with the flying controls operated by two handles below and ahead of his shoulders. The handles could be pushed forwards and pulled back together to move the elevators, tilted from side to side together to move the ailerons and moved laterally together to operate the rudders. Twin throttle levers to control the engines were mounted on the left side of the cockpit. There was also a padded chin rest to hold the head in a position to look straight ahead through the transparent nose of the aircraft. Our task was to fly the aircraft from the prone position and assess the practicability of this. All flights were made with another pilot in the conventional cockpit to operate the conventional controls when required. I and my colleagues made a number of flights from the prone position and found several major problems. Firstly it was very tiring to stay in the required position and attitude looking forward through the nose. On take off it was very difficult to keep straight along the runway due to lack of any reference point forward of the pilot’s viewpoint although we did find that painting a vertical line in the nose transparency was some help in this respect. The operation of the rudder control by hand was awkward and difficult to co-ordinate with the other controls. I did manage to achieve safe flight from take off to landing without having to fall back on the safety pilot but our general opinion was that this was not a practical way to control an aircraft. The most unnatural and alarming manoeuvre was spinning which involved plunging head first watching the ground below rotating at high speed and unable to apply proper corrective rudder due to the poor mechanical advantage of the hand operated control. This was where the safety pilot was essential!