NEC ECSC - Vested Material - at what point does the Employer become liable for insuring vested material?

Under the NEC3 ECSC contract we have placed an order for the procurement and installation of materials, we have made a vested payment upon Contract award. At which point does insurance transfer from the Contractor to the Employer for the vested material?

Under the ECSC, there is no formal procedure in relation to ‘vesting of materials’, unlike in the ‘full’ contract versions. This does not change the insurance obligations, however, whereby the Contractor is to provide insurance for ‘Loss of or damage to … Materials’ from the starting date until the Defects Certificate has been issued.

The ‘vesting’ procedure essentially allows for an ‘advance payment’, otherwise payment would be calculated in accordance with the definition of Price for Work Done to Date, essentially for completed items in the Price List.