He says they are not obliged to provide a replacement.
Their Warranty begs to differ:
Warranty Cover • Guarantees repair replacement or adjustment, free of charge, by an Authorised Repairer, of any part which fails during the warranty period, as a result of a manufacturing or material defect.
Extra Expenses, Damages & Losses Under the terms of this warranty, MG Motor UK are only liable for the repair or replacement of original parts by an authorised MG Dealer or an authorised MG Repairer, that are defective in material or manufacture.
It is a manufacturing defect confirmed by the fact they are working on an alternative,
His boss needs an email I think.