Britain’s takeover regulator has given mining group Xstrata an extra week to decide whether to accept the $36 billion revised offer from Glencore, prompting jitters over what is the latest twist in a seven-month saga.

The unexpected extension – granted at the request of both firms – surprised the market, which had been expecting Xstrata to announce its decision by Monday at the latest.

Analysts attributed the delay to talks around management incentive schemes and the nomination of Glencore’s chief executive for the top job at the merged entity, rather than Xstrata’s, which was proposed by Glencore in what it called its final offer, earlier this month.

Shares in Xstrata closed down 4.2 per cent in London while Glencore fell 1.7 per cent.

“The extension was requested to enable Xstrata’s independent non-executive directors to take full account of feedback from consultation with key Xstrata shareholders,” Xstrata said in a brief statement.

It has until October 1st to say if it will recommend Glencore’s offer to shareholders, having first backed a lower offer in February.