OP, IMO nothing has changed. The excess charge is payable by
Excess charge
7.—(1) An excess charge of £30* shall be payable, in accordance with paragraph (2), in respect of any vehicle which is allowed to remain parked in contravention of regulation 3 or 4.
(2) The excess charge shall be paid to the Secretary of State, or to a person authorised by the Secretary of State to receive such charge on his behalf, by the person who parked the vehicle in the Park within 14 days of the date of a written demand for the same.
(3) Payment of the excess charge in accordance with paragraph (2) shall preclude proceedings being commenced for contravention of regulation 3 or 4.
*- increased to £80 on 2010.
If you weren't driving then this is a defence against any claim against you, should you get one. I say should you get one because you've posted an ECN, but it's not for you, it's for the driver. Therefore it's for the driver to decide. If the driver is also the registered keeper and if a demand - they refer to NTO but there's no such beast under these regulations- is issued to the RK then they should come back here.
As regards the underlying failure to comply with the regulations which were communicated via the sign, this is correct: payment was required but not made. Had the driver looked diligently they would have found the machine.
At this stage the person holding the ECN could hardly challenge that they weren't!