The Channel Tunnel operator’s London-listed shares lost more than 17 per cent of their value on the warning from the Autorité des marchés financiers (AMF).

The shares more than tripled in value this week after regulators lifted a suspension. Trading began on Tuesday morning, opening at 25.5p. They opened on Wednesday at 41.9p, breaching 100p during the day before closing at 77.5p.

The surge came after the group confirmed that shareholders had given their backing to a deal that will save the Anglo-French group from collapse.

Eurotunnel shareholders, including those who have not already accepted the rescue plan and those who bought shares this week, have until June 14 to surrender their holdings. In exchange they will receive a stake in the new group that will take control of Eurotunnel’s assets.

The sharp rise in the shares could, according to one analyst, be the result of hedge funds buying shares. They are thought to have built up significant “short” positions in the transport group, betting on a collapse in the price if the rescue deal failed. Such positions are closed by buying shares.

The AMF’s warning yesterday left the shares down 21½p in afternoon trading before they finished the day down 13½p at 64p.

The group’s Euronext-listed shares, which are traded in Paris, closed down 25c, or 18 per cent, at €1.10.

The regulator said it was necessary “to call the attention of investors and financial intermediaries to the atypical nature of the current situation”.

Eurotunnel’s shares were suspended early last week after the deadline had passed for shareholders to accept the terms of a rescue package that will see the group’s massive debts slashed.

They were suspended in London soon after the Monday deadline, pending the result. AMF revealed on Friday that shareholders holding some 87 per cent of the group’s equity had accepted the rescue package, which will see the group’s debt cut from £6.2 billion to £2.8 billion.

The debt-for-equity swap will see shareholders who tendered their holdings issued with shares in Groupe Eurotunnel, which will take on Eurotunnel’s concession to run the Channel Tunnel until 2086.

Shares in the new group will be listed on the London Stock Exchange and Euronext once formalities have been completed.

Some founder shareholders have opted to hold on to their existing Eurotunnel shares to preserve the perks that date from the group’s flotation 20 years ago.

Early shareholder privileges included unlimited £1atrip travel through the tunnel. More recent shareholders receive a less generous 30 per cent discount on up to three return trips a year. As part of the rescue package, all shareholders in Groupe Eurotunnel will qualify for the 30 per cent discount perks.

Eurotunnel has suffered from crippling interest payments on its debts, compounded by weaker than expected traffic figures in its early years.

The group’s early business plans assumed that the tunnel would take all cross-Channel business away from the ferry companies.