This is a 2010 model Corsa VXR.

The accelerator pedal is quite stiff after the first inch or so of travel. It's not exactly hard to press, it's more notchy/sticky - it's hard to make minor adjustments to the amount of gas. Seems a bit all or nothing. This is a fairly nippy little car so it can make smooth progress a bit difficult.

The car has only 5000 miles on the clock - it never used to be like this.

I know there's no throttle cable involved. It seems worse after rain, which is confusing. After a dry spell it is back to normal. It doesn't seem as if water is leaking in.

Vx dealer 'found no faults on computer' - not sure how the computer relates to a physical thing like an accelerator pedal not moving freely. It has been in three times and they say they can't fault it.

Any ideas?