The troubled support services group has until June to buy back the holding from consortium partners Jarvis and Bechtel, but the general view is that it will be unable to do so because of financial difficulties.
Jarvis and Bechtel lent Amey the £60m stake last month to ensure that the PPP contract would be signed, and gave it six months to buy the stake back.
However, Amey was able to raise only £29.1m in cash this week from the sale of eight of its PFI equity investments to Laing. This was a long way below their commercial price – said by some to be £150m.
Analysts estimate that by June Amey will still have debt of about £150m and that it will owe twice as much as its investor capital, giving it a gearing of 200%. In these circumstances it is unlikely that any bank will lend it money to buy back the stake, especially when the firm is trading at a low share price of about 30p.
A senior City analyst said: "Amey simply will not be taking up its option on the London Underground. I reckon it's nigh on impossible. The banks will not let it."
An Amey shareholder agreed. He said: "I don't see how Amey will find the £60m it needs to fulfil its London Underground commitment."
An spokesperson for the firm denied the claims and said the group would be able to raise the finance.
Many shareholders believe the break-up of the firm is inevitable, although a rumour has circulated that it might merge with support services group Atkins, which is also in difficulties. This has been discounted by most City sources.
Swiss corporate raider Tito Tettamanti's Sterling Investment Group is now the single largest shareholder in Amey. The acquisition of 750,000 shares on Tuesday, took its stake to 15.26%.