Shares in National Express plunged more than a quarter on Friday after the Spanish-led consortium bidding for the bus and rail operator withdrew its £765m takeover offer, dealing a blow to the company’s biggest shareholder.

CVC, the private equity firm, and the Cosmen family, which owns an 18.5 per cent stake in National Express, had been due to finish due diligence by 5pm on Friday before making a formal offer. Last month the consortium raised its indicative offer from 450p a share to 500p a share.