Here is a very interesting article about vapour locking:
http://www.canadiandriver.com/articles/jk/at_000814.htm
Another thing is my car uses 4 star leaded fuel. This was banned by the EC in 2000 so I have to use LRP (lead replacment petrol), I've never had a problem with this as I don't do high speed or a lot of miles, LRP isn't good for the engine at high speed.
Now it seems that LRP is being phased out, Shell have stopped doing it in my area and this is where I used to buy it. I now have to go to the BP station and buy 'lead free' petrol - this isn't unleaded but lead free, confused I know I am.
Now I've only been using this new petrol for three weeks, although I've been on holiday a couple of weeks ago and did 600 miles without a problem.
Could my problem be vapour lock especially after reading the above linked article?