OK, that was embarrassing. I was driving into work yesterday when I saw in my mirror that the car was emitting a huge cloud of white smoke. Picture a WW2 destroyer laying a smoke screen and you are getting close. Water temp shot up, and I had to pull over. Not easy on the M60, but there's a hard shoulder on the J16 slip anti-clockwise, so I pulled over there. Called the RAC (got to get your money's worth) who arrived about 50 minutes later (at some point "Junction 16" got translated to "Junction 18"). The guy quickly found a fair-sized split in the top radiator hose. He filled the car up with enough water to drive on, and I drove a bit up the road to find a proper spot for a repair, trailing a huge white cloud. He managed to bodge a new centre section to replace the broken hose, and i got going again. New hose ordered, now I jest need it to arrive so I can fit the thing.