Yes, it's a real gibbet. Today was a day I spent out and about retracing some of my past. You can see that the weather was HORRIBLE (this is normal: those grey skies seem to be permanently fixed. The climate has changed and there will never again be a blue-skied, sunny English Summer. I hope that's not true, but it certainly is bad at the moment.)
In researching the history of the Caxton Gibbet I came across one those amazing things that the Internet has brought to us - a complete listing of war-time airfields operated by the Royal Air Force and the USAAF in Britain PLUS the REALLY BIG THING, photographs of all the various different designs of control tower to be found on the old air stations.
It seems that there was once, now long gone, an "RAF Caxton Gibbet" - no doubt a bomber airfield; just one of the many scattered across Eastern England between 1939-45, and now lost forever, just like the English Summer.