So within the scope of parking enforcement this matter has nothing to do with you!
But you posted last year: I've written to the lease company and they've confirmed that they've passed on my details to Harrow Council
OP, to be clear, if the lessee is a company then only the company may make reps and appeal, you as an individual may not. You may draft for them and even represent them subject to holding the necessary written authority by the penalty will never be yours.