You'll have to find the landowner from the Land Registry. It's not 'classified information' - they just don't want to tell you. These people are crooks after all.
No point beating about the bush with your letter - be firm:
QUOTE
NOTICE OF INTENDED COURT PROCEEDINGS
Dear Sir/Madam,
On [date] a clamp was placed on our car [registration] which was parked by St Peter's Road in Bournemouth town centre.
I am writing to demand payment of the sum of £120.00 which I was forced to pay under duress in order have the car released from this clamp.
Signage marking that the area in which the car was clamped was private property was far from prominent and was not seen by myself or my wife, even though we looked around the area to check for parking restriction signage. Case law settles that an appellant who had not seen signs warning about clamping could not be held to have consented to, or voluntarily assumed the risk of his car being clamped (Marina Helen Vine v Waltham Forest London Borough Council (2000)). Furthermore, I have not entered into any contractual agreement with the land owner to pay any parking charges.
From Marina Helen Vine v Waltham Forest London Borough Council (2000): "The act of clamping the wheel of another person's car, even when that car is trespassing, is an act of trespass to that other persons property unless it can be shown that the owner of the car has consented to, or willingly assumed, the risk of his car being clamped. To show that the car owner consented or willingly assumed the risk of his car being clamped, it has to be established that the car owner was aware of the consequences of his parking his car so that it trespassed on the land of another."
I deny entering into any contractual agreement with yourself or the land owner. Even if a contractual agreement were found between ourselves (which is denied), no direct, quantifiable loss has been suffered by the claimant, hence the amount recoverable under contract law, as damages, would be zero.
Unless full payment of £120.00 is made to the above address within seven days, Legal Action to recover the debt will be taken against you without further notice. Should you respond to this letter within the next 7 days, I also request your SIA Registration Number. As you will be aware, it is an offence to operate a clamping business without one.