I was going to stop off for a minute while I grabbed something from a shop when I saw a simple but possibly effective PPC sign and was put off. It just read "Private Property" , "There is a charge of £100 per day or part thereof for parking in this area." and was signed clearly and well-lit.

Now, I'm sure I wouldn't have been caught in 5 mins - or that it would ever get to court - but I chose not to park there, in part just because I was impressed compared to most PPC signs, and the risk I'd be forced actually to pay up.

My question: ignoring issues about a PPC being able to issue tickets on behalf of occupiers, and proving who the driver was, could this actually represent a valid contract for parking?

If they genuinely want to charge £100 a minute to park there, they are entitled. But a court would find it difficult to believe a person would accept it and that the act of parking was acceptance. By all means put somebody on the land who explains the contract in person and gets a signature from the driver.

The high charge sounds like they want to prevent ANY parking.

Yes the signage sounded clear and a landowner is entitled to prevent unwanted parking on his land, but I would have more respect if the sign spoke to me like an adult and not someone who'd been released from prison that morning.

Remember by deeming that enforceable, a sign on my driveway saying "Toe charge in operation. If you place a little toe on this land you are contractually agreeing to pay me £100,000" would be equally valid.

I would guess there could also be some HMRC, business rates, planning permission questions for landowner, since the sign appears to invite parking for £100 (a day?)

yup. start looking somewhere like this
www.voa.gov.uk/instructions/chapters/rating_manual/vol5/sect200/frame.htm

which no longer works - seems they have changed the site.
it may still be in the web archive

you used to be able to do quite useful checks...

can start digging here
http://www.voa.gov.uk/instructions/chapter.../vol1/Frame.htm

vol5 link they provide ( http://www.voa.gov.uk/instructions/chapter.../vol5/frame.htm ) gives me "The page cannot be found"

Fair enough Bama, but I guess that wouldn't affect the validity of the contract, it could just be used to make their life (rightfully) harder.

Would they really need to pay business rates / get planning permission for the occasional unexpected parker? Are people who currently advertise their driveways on the web doing wrong? I was thinking of doing that haha, better be careful.

With regards the 'toe charge' ide to Alexis, I suppose the point would be that given the extent of the charge, it would be difficult to prove consideration / acceptance (and if indeed it could be shown that the trespasser examined the sign in detail it would likely stand). A £100 parking charge, while high, is not completely unbelievable and somebody may well accept on the basis that they think they wouldn't have to pay?

That may well be utter tosh legally, and perhaps its about unfair terms in consumer contracts (which I guess is what stops companies placing 'we now own your house clauses' in online terms and conditions that you have to tick ). Would a £100 charge fall foul? Stated that clearly, I suspect not, but am no expert.

Anywho, don't want to give them too many ideas. Not that I see PPCs being able to bring themselves to write clear and reasonable notices - misrepresentation and words like 'illegal', 'fine' and 'unauthorised' are much more fun.

This sort of thing would be covered by SOGASA (I think). There, it holds that contracts for the supply of goods and services shall be for a "fair and reasonable price".