Can anyone provide some clarity on the difference if any if the PM were to use either of these clauses to notify rejection of the submitted programme?
Neither - those clauses state the rules on which the response should be given i.e. that it has to be responded to, if rejected clear reasons why it is rejected and that the communication has to be separate from other communications. The clause that should be referenced in the response for rejection of a programme is clause 31.3, for which there are four reasons they can reject.
It is worth pointing out that NEC4 now says if the Project Manager is rejecting a submission, they should state the reasons why IN SUFFICIENT DETAIL TO ALLOW THE CONTRACTOR TO CORRECT THE SUBMISSION (the capitalised bit being the new additional words). This makes it clear they have to give specific reasons why rejecting to allow them to correct it, not giving high level reasons e.g. your programme is not realistic.
I think my question wasn’t clear, I get that 31.3 is that clause that should be used to reject but which of the clauses are used to communicate that rejection? Can the PM communicate using either?
13.4 and 13.7 are just the rules around that communication. Most projects now used a cloud based system to manage their flow of communication e.g. FastDraft and within that system there will be a response form built in to respond to any type of communication under the contract.
Simsai, the rule in clause 13.7 applies to any clause that requires someone to notify; the rule in clause 13.4 applies to any clause that requires reasons to be communicated. So the notification from the PM that the programme is not accepted should be communicated separate from other communications (13.7) and should cite one or more of the reasons given in clause 31.3 but in sufficient detail that the Contractor can comprehend the reasoning and address it in its resubmission (13.4).