If your car under finance has been clamped on private property that is not your home, the bailiff is breaching regulations, giving you grounds for court intervention.
If your address has changed, identify which council (Southwark?) the bailiff is acting for and request the PCN number. Using this number, contact the Traffic Enforcement Centre at 0300 123 1059, providing the postcode from your previous address in the security check. If successful, the warrant may be a "defective instrument".
Before applying for court intervention, give the bailiff and the council a Rule 6 Notice of Application to allow the bailiff to remove the clamp.
Please confirm the address on the warrant, ownership, and location of the clamped vehicle for further advice.