My biggest worry is that the ignorant individuals could call this "hacking" and initiate proceedings that could make your life very difficult. More to the point, England has shown itself to have some really stupid "hacking" prosecutions in the last decade. I would make sure you haven't opened yourself for such charges.

As it stands, I would not have started the additional work in October without further contract and payment schedules agreed to. If I had not done that, I would have been sending invoices all along and stopped work a lot sooner than 14 weeks.