Firstly, is the car in your private names or in a limited company name. If it is in your private names and the amount loaned is under �25,000, then the agreement is a 'regulated' agreement and you have a lot of rights under the Consumer Credit Act. If it is outside the scope of the act (over �25k or ltd company) than you have none of these rights.
If the agreement is a loan agreement, you do not have the benefit of the 'thirds rule' mentioned previously.
Get a copy of your agreement and along the top should be the words "Hire Purchase agreement regulated by the Consumer Credit Act 1974".
If it does not say that, then you will have different rights.
Finance companies want their money - simple as. They will certainly imply (and quite often lie) about rules and regulations. and what they can / can't do to try and intimidate.
If you are constantly late paying your HP off (and have paid a third), then as previously noted the finance company will need a court order - and to be honest, the court will probably not grant one if you defend yourself and show that you are attempting to pay.