AN Investment company controlled by one of the world's wealthiest royal families last night denied it had any power to influence the rent bill which has led to the crisis at care home giant Southern Cross Healthcare.

The GMB union has claimed that the Qatar Investment Authority (QIA), which was established by the Emir of the Gulf state in 2005, is the ultimate owner of NHP, Southern Cross's biggest landlord.

But last night QIA, which claims on its website to "apply the highest ethical, moral and professional standards of conduct" in all its undertakings said it had a "very limited connection" with Southern Cross and no involvement with setting rents.

Southern Cross, which rents the vast majority of its 750 homes after selling most of its properties and leasing them back, has since seen those rents rise faster than the income it receives for peoples care.

The Darlington based firm, responsible for the care of 31,000 predominantly elderly people, has blamed these rising rents for placing it in a critical financial position.

Southern Cross is trying to persuade landlords to cut rents as many of the lease deals it signed, including those with NHP, are understood to have around 30 years left to run. The GMB, which has staged demonstrations against Harrods owner QIA claiming its should cut "the sky high rents", yesterday said the Emir of Qatar should "face up to his responsibilities and meet the costs of unwinding a property deal that has gone spectacularly wrong."

Last night the QIA said it only had an indirect interest as a limited partner in the Delta Fund, the ultimate owner of the NHP Group.

It said: "This interest does not give it the right - and never has - to manage, influence or control the operations of the Delta Fund, NHP or Southern Cross.

"QIA does not, and has never, set or collected the rent charged to Southern Cross care homes, for the reasons detailed above. QIA does not see and has never seen any of the rental income.

"This income will be used by NHP to meet its expenses, including the servicing of its debt."

The QIA's chairman is the crown prince Sheikh Tamim bin Hamad Al Thani and its chief executive is Sheikh Hamad bin Jassim bin Jabr Al Thani, a fellow royal and the Gulf State's Prime Minister.

The financial difficulties at Southern Cross have left it trying to negotiate rent cuts with its landlords since September.

The agreements it signed have seen rents rise faster than the fees it receives for residents' care from local authorities, on which it is heavily dependent.

Having admitted last month that it was in a critical financial position and could not afford to meet its future rent obligations in full, a week ago the group was granted four months of breathing space by its landlords, during which time it will defer 30 per cent of its monthly rental payments.