The Sainsbury family have written to the Qatari Prime Minister to emphasise their opposition to a highly leveraged buyout of Britain’s third-largest supermarket chain by his investment fund, Delta Two, sources told The Times yesterday.

It is understood that Lord Sainsbury of Turville and Lord Sainsbury of Preston Candover (David and John Sainsbury) wrote last week to Sheikh Hamad bin Jassim bin Jabr al-Thani after a meeting between the two parties in Sardinia this month.

They made it clear in the letter that they would not back any takeover of Sainsbury’s that left the group too heavily indebted or that sold off any of its lucrative property portfolio.

A source close to the situation said last night that the family were furious that they were being kept in the dark over the £10.4 billion bid. He said that Delta Two, which is advised by Paul Taylor, had said that it would contact the senior family members with its bid plans after the Sardinia meeting.

However, despite approaching Sainsbury’s board with a 600p-a-share offer last week, Delta Two has made no further contact with the family, the source said. “[The family] told all their concerns to Delta Two and they were to come back to us with their plans for the company . . . but they didn’t,” the source said.

“So far the only thing that’s clear about the offer is that it will include a level of gearing that’s similar to the other [CVC] consortium and an underlying assumption that it’s a property play,” the source added.

The Sainsbury family, who among them own about 18 per cent of the retailer, is key to any successful takeover. This year the members blocked a 582p-a-share bid approach from CVC Capital, the private equity firm, saying that they would not consider any offer below 600p.

In addition, the family would consider a bid only if the management team were left intact and if an agreement were reached with the pension trustees. Last week Delta Two said that it would use about £4.6 billion of cash to buy Sainsbury’s and borrow about £7.8 billion of debt, which would sit on the company’s balance sheet after the deal.

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