Note that this new sill is made from softwood not hardwood as specified in the Armour Hart contract specification. Also note that there is no drip groove on the underside of the sill which is essential to ensure that rainwater drips off the edge of the sill. A cheap sill as illustrated will cost around £10 from Travis Perkins timber merchants whilst a hardwood sill with a drip groove will cost around £40. There are over 1,500 windows on the HHGE flats with an average of 7 per flat.
If all the sills need replacing the cost could be well over £45,000 extra. No wonder the contractor is skimping on the quality of the materials.