parking from a different angle

[Dixy]

Following the trespass thread and countless others on parking infringements I would welcome the collective views on how to deal with this problem.
I run a small specialist retail business for the elderly and disabled, there is a small private car park for clients, it has a gate and is secured at night but during the day it is open. It is not lined or marked in any way as my clients often need to just abandon the car and others stay in the car and toot for us to go out to them.
About once a week some chancer will just park up and disappear, our normal action is to block them in with a vehicle and when they come in asking for it to be moved we suggest they put a folding donation in the charity box whilst we move the blockage.
I am beginning to get pissed off, if a customer does not come in because the car park is full it could cost me a lot.

[Hackney]

Barrier on the car park and intercom?

If a proportion of your customers need assistance anyway the no expense system is a sign on the closed gate, saying phone (or pip) for assistance.

[surveyor]

Basically nobody cares. There is no solution that will not cost you money.

The legislators had limited vision when they banned clamping with no practical alternative way to police private parking. The immediate disruption of clamping was what put people off. A bit of paper is no deterrent.

I think a sign, "Customers of xx are very welcome to park here. Non-customers should note that that gate is closed at random internals and acknowledge that they may be inconvenienced".