The Enforcement Notice increases the penalty charge to £160, so are you prepared to risk the extra £80 ? If you're not, then it's pay-up time.
On the other hand, if you are prepared to take the 'double-or-quits' gamble, there is a a little known quirk of the London Local Authorities Act 1996 under which the PCN was served, which means their CCTV evidence, (their sole evidence), could be declared void at an adjudication at London Tribunals.
Our Hippocrates has won some on this basis, so hopefully he will explain it.