If amounts were certified prior to the Project Manager issuing a termination certificate then the provisions of the 'Construction Act' would still apply and payment would have to be made by the final due date, unless a formal notice was issued within the appropriate timescales.
The assessment by the PM after 13 weeks relates to the amount due on termination.
As a matter of interest (no pun intended) have a look at the Late Payment of Commercial Debt Regulations 2013 and calculate how much compensation you should be entitled to for late payment.
Most NEC contracts have clauses dealing with such a situation (late payment) but, from my previous research into this matter, it is more than likely that they are not actually compliant with the requirements of the Regulations, especially the amount of interest stated.
The assessment by the PM after 13 weeks relates to the amount due on termination.
As a matter of interest (no pun intended) have a look at the Late Payment of Commercial Debt Regulations 2013 and calculate how much compensation you should be entitled to for late payment.
Most NEC contracts have clauses dealing with such a situation (late payment) but, from my previous research into this matter, it is more than likely that they are not actually compliant with the requirements of the Regulations, especially the amount of interest stated.