That's funny, I always thought it was general knowledge.
It was general knowledge, it was however illegal as both Lewisham and the GLC had declared their areas Nuclear Free.
there was speculation on how exactly you arrest a train.
Some years later Mark Thomas did a great program where he turned up at Dunginess with a load of Army reenactment people with a tank, armoured cars, people in radiation suits and they then 'protected' the flasks being loaded.
If the Iranians ( or the local shop lifter ) had wanted a couple of tonnes of processed nuclear fuel then it was available to anyone who could drive away with the stuff.