Our dryer seemed to be taking ever longer to dry! Googling it became clearer that maybe the dryer vent was blocked. Further googling and I found Dryer Vent Cleaner, run by Ian.
I had thought my dryer vented through a wall. It turned out that it vented through the roof. The vent was completely plugged as there was a screen over the vent which clearly prevented any lint escaping.
Ian (very pleasantly) found the problem when he got into the roof space (on a hot day), modified the vent, completely cleaned the lint from the ducting (there was a lot!), and reconnected everything better than it had been before. He also had a great gauge which measured back pressure in the dryer so the (vast) improvement was easy for all to see.
So why not "10"? Well, ideally Ian said we needed a better designed roof vent. Sadly he could not install one as our roof was a bit too steep and high to be safe.
However, if you want a guy who knows what he's doing, who puts things right and leaves the place clean and tidy then Ian is your man! (We'll get a roofer to replace the vent sometime!