JCT: Notice to quit

Under a current project with a public sector employer, we have submitted our valuations on time, they have been recommended for payment by the Client QS as correct, They have been certified by the Architect, the client has been invoiced accordingly. The client has came back after 31 days from the 2nd valuation being certified to say that the invoice should be given to the architect and NOT them as a client.
We are now due payment for 2 valuations to be clear.

What is my best redress? 7 Day notice?

JCT 2012 With Quantities

Assuming that there is not doubt who the Employer in the contract is, and that there are no amendments to the standard building contract that say to the contrary, the Employer is liable to pay the Contractor the certified amount as they did not issue a pay less notice in accordance with the contract (clause 4.12.5). You do though need to check the contract to see if an invoicing procedure has been inserted that makes submission of an invoice to the Architect a condition precedent to payment being made by the Employer.

Assuming not, then you are entitled to simple interest on the late payments (clause 4.12.6) and to give a 7 day notice of intention to suspend (clause 4.14.1).

Better to take this action now, in the early stages of the contract whilst the stakes are relatively low, rather than wait until you have serious cashflow problems later on.