Not enough power to pull caravan?

What a wonderful contribution to this debate! Thank you so much Paul. I think you may well have identified the cause of my problem that morning. It's more likely than ever that this will turn out to be "one of those things".

I am heartened that it seems there's nothing wrong with the car. On that day I thought it was the car, evidenced by it not revving beyond 2,500 rpm in neutral. I thought the car had gone into 'limp mode'. My wife bought a Seat Leon (= VW Golf) of a similar age and it developed a fault that put the car into limp mode. Turned out to be some sensor or other which was replaced simply, under warranty. I thought my car had developed the same fault. Now I'm happier, and looking forward to doing some caravan towing - more than a 5 mile round trip - in the spring and summer and beyond.

BTW I have been caravanning only about 5-6 years, and have come to the conclusion that the engineering of caravans is nowhere near the standard of that of cars. Things keep breaking. Even German companies ( especially Alko) produce products that are imperfectly designed. Maybe English caravans are better, but I doubt it.

Alec