There is fierce competition among bar operators

The pledge came after founding family investors in the company attacked the Thorium bid for undervaluing the firm.

The bid vehicle, set up by GI Partners and involving Yates' management team, said it was extending its 140p-a-share offer for Yates for another week.

The bidders have convinced 26.6% of Yates' investors to back their bid, but need to secure 90% to force a sale.

Yates' founding family members - who hold around a fifth of the group's shares - have now challenged Thorium to increase its bid claiming it fails to take account of the future potential benefit of Yates' �18m refit of 98 of its pubs.

The founders have also threatened to retain their stakes even if the bidder wins over the majority of its investors.

'Attractive price'

However, Thorium refused to up its offer as it extended its deadline to 29 July. It also argued that the founders had failed to show how the revamped pubs would benefit the chain in the future.

The row has broken out almost a month after the group's independent directors backed the buyout offer, with chairman Mike Hennessy describing it as an "attractive price".

Bolton-based Yates, which employs 4,000 people and has 129 Yates and 23 Ha!Ha! outlets, has been trying to reverse a sales slump amid tough trading conditions.

It has seen annual profits slide from �15.6m in 2000 to �10m in 2003.

But last month, its full year results seemed to indicate a slight change in fortunes with full year profits inching up to �10.6m.

By mid morning, shares in Yates stood 0.5 pence higher at 131.5p - still significantly below Thorium's offer.