The Biker:
The american trucks on the A14 run from the US base down there and deliver all over the UK - they come to my place most weeks and bring trailers that are shipped over from the states. They used to GMC Aerostars but have changed some of them to cab over Macks. They did have a day cab Iveco Eurostar 6 wheel unit at one time.
A lot of these motors are based at Mildenhall USAF base in Suffolk. They are owned and run by the US equivalent of the ‘Naafi’ - ie. the supplies & logistics department. As you say they used to be GMC’s (often with a day cab rather than the typical US 14’ caravan on the back of the cab), which If my memory is correct were the US version of the old Bedford TM. I have also more recently seen some MAN’s in dark blue with 4wd (or very large wheels/high suspension) on US plates also.
The closer you go to Lakenheath/Mildenhall the more US motors you see, even US military police cars…
Whether it’s true or not I don’t know but the opinion locally is that the US bases are in such a parlous state financially that they are operating on relatively modest budgets these days since the cuts following the cold war.