The chap who put the wheels on did not tighten the nuts adequately.
Fortunately I was driving slowly . . . . . . it has started to rain.
It was a simple matter to remove a nut each off the remaining wheels and get home . . . .. another two hundred yards.
I then drove the two mile trip back to the starting point (long story) , I found one about twenty feetv from where the wheel came off.
I then drove at about 4 mph back again looking for the nuts.
I had heard a bit of knocking from that wheel at the start of the journey. I even stoped to see what it was.
Then a miracle I found the other three nuts. The last one in in the middle of the road - the BMW that went past when I was there looking for the last nut must have knocked it into the road again.
Worse than the embarrasment of chasing my wheel down the road was the fact that one of the wheel studs punctured the tyre on its way past 
