Just back from 4 weeks holiday to find the keyfob won't unlock the car, so tried to use the emrgency key but unable to turn the lock. Gave it a good spray with WD40 but no result.

Question: if I hold the key in a pair of pliers, how much force can I exert before it breaks?

Hmm, not much, the lock contains plastic parts, are you certain the key is the correct one, have you another fob you can try the other key from?

Yes, I have two fobs, both keys appear identical and neither will budge.

I would try something on the key then, go gently though, I suppose it's never been used and 5 years is a long time for it to sit doing nothing.
Maybe wise got others to try theirs no and again to keep it free.

Good luck

I would keep spraying a lubricant in not necessarily WD40 and give the lock a good old bash push and pull on the door,can't see what else there is to do.

Thanks, I'm in!

I sprayed a lot more WD40, and used a pair of pliers to rotate the key back and forth and it gradually started to loosen.

Long shot I wonder if heat from a hairdryer may help ?

That's good to hear.