Silent UFO craft observed flying close to Nuclear Installation Thetford GB 3/2001

From Jan 2000 to June 2001, I served within the RAF Regiment as an Armed Guard at a Nuclear Warhead storage site at Royal Air Force Honington in Suffolk, UK. My memory for the date and time of this is a little hazy, but I can remember exactly what I saw that night and I was not the only witness. It was around 3 am in the morning, me and a colleague were returning to the site after conducting a three hour off site mobile patrol. We parked our vehicle just outside the main gate to the site and started moving towards the first of three pedestrian access gates when we noticed what we thought to be a low flying aircraft on a course that would take it directly over the Nuclear installation. Just to point out that RAF Honington was not a flying base, it was a very rare thing to have any air traffic at the base at all during this period. There was also a strict no fly zone in place over the Nuclear site to all Military and civilian aircraft. We estimated the UFO craft to be at around 800 - 100 ft in the air. The size of the UFO craft was probably similar to that of a Stealth Fighter. We couldn't make out a definite shape, but there were three white/yellow lights creating a triangle with a red light in the middle (cant remember if this flashed). We ran over to an external phone that was just outside the gates and alerted the control room that a plane was just about to fly low over the site. As we watched the UFO craft approach the site from the South East (see attached pic) it veered off at the last minute towards the West, avoiding the site and disappeared out of view. Up to this point we thought it to be no more than a military plane from nearby RAF Lakenheath that had gone off course, it wasn't until the UFO craft came close by us as it turned off to the West that we realized it was completely silent, the whole area had become strangely silent also. This event was logged in the Control Room DOB though at the time we didn't make a big thing of the silence for fear of ridicule. After this we racked our brain as to what it could be, coming to the conclusion it was either a glider (which I didn't know could operate at night) or a top secret aircraft being flown in to Lakenheath.