I don't know about over there...
But on this side of the pond, if the ground tanks the gas is stored in and pumped from aren't regularly cleaned and maintined, they build up all kinds of sludge and grime. Each time a truck delivers more gas, it stirs up all that grime. If you fill up around the time of the delivery, that sludge will get in your tank and significantly reduce your performance.

So the moral of the story is: never fill up within a few hours of a tanker delivery. Try different stations and pay attention to your car's performance on that tank of gas. Eventually, you will find a station that maintains their pumps and you shouldn't have any problems.

There are also additives you can use to improve performance.

I got lucky. The most well maintained tanks in town are at a gas station that also has some of the lowest prices. It is only 5 miles out of my way, but well worth it in the long run as it saves me on maintenance.

Edit: I can't believe a GIRL was the first to explain your problem. You guys should be ashamed of yourselves.
( flirting with badgers What? It sounded good at the time., Wed 19 Nov 2008, 17:06, Reply)