Investors in Expro, the UK oil services provider, will today ask a judge for a lengthy delay in approving a £1.8billion takeover bid by a private equity consortium to try to let a rival suitor, Halliburton, the world's second-largest oilfield contractor, to bid again for the company.

The case could threaten the Takeover Panel's authority to enforce bid deadlines and undermine its efforts to regulate schemes of arrangement.

Two hedge funds, Mason Capital and Sandell Asset Management, which between them own 15 per cent of Expro and are seeking the delay, are angry that Expro rejected an offer by Halliburton in favour of a lower bid by Umbrellastream, a consortium led by Candover, the private equity firm.

The shareholders will ask the High Court to delay for two weeks approval of a scheme of arrangement facilitating a takeover of Expro by Umbrellastream, which could open the door for Halliburton to re-enter negotiations.

Approval of a scheme of arrangement is normally a routine legal procedure but in Expro's case it has already been delayed twice this week as lawyers for shareholders, the companies and the Takeover Panel argue over whether the deal should proceed.

Arguments have centred on Halliburton's withdrawal from bidding for Expro on Friday, after independent directors rejected its offer of £16.25 a share, even though it was 10p above Umbrellastream's offer. The directors felt that regulatory hurdles faced by Halliburton would cause delays that meant its offer was effectively worth less.

Under Takeover Panel rules, withdrawing bidders must not bid again for six months. Lawyers watching the case fear that if Halliburton succeeds, it may encourage losing bidders to bypass the rules and go to court to pursue their targets. The Panel, fearing for its authority, opposes adjournment.

Halliburton is relying on a complicated legal argument that its withdrawal was conditional on the scheme of arrangement not being delayed for 14 days or rejected by the court. It is that condition that shareholders are now seeking to exploit.

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