Does the company have a VOR policy - ie a list of faults a driver can VOR for and faults that shouldn't be VOR'd? If the a/c is on the VOR list then you're sorted. If not look at H & S policy re max and min working temps. I assume that temp in cab is around or above 30c so you may be able to argue it. However I suspect you'll probably just have to keep driving in which case get some oral rehydration salts sachets from chemist/supermarket mix them in several bottles of water and drink during shift. Also freeze some bottled water overnight and take with you as that'll take most of day to defrost leaving you with cold drink.

You don't need to fork out any money for solicitors fees! The small claims track is very easy to do yourself, you get an info pack with it all telling you how to go about making the claim. IMO I would never tocuh a solicitor again, there is nothing they do which with a bit of research and knowledge you can't do yourself.

Update:- Good News, they've cancelled it. Father got a letter this morning 'We are writing to confirm that this case will now be cancelled'. My dad suffers from various conditions, he was actually receiving treatment at the time, so used the Equality Act 2010, in that he should be allowed more time then a normal person. Also the car park in question has a one fits all policy for the users of the car park. That the car park has no kiosk and they use cameras so that left my dad with a disadvantage as he could not inform them. The onus is on the service provider to make reasonable adjustments.

100% she has grounds for a full refund. This is how backstreet dealers operate unfortunately. They rely on the buyers ignorance or lack of knowledge of trading law. Thats why you'll see most saying they cant do anything outside of their silly warranty periods.