Ah!
"The facility - an alternative to a traditional mortgage - conforms with Islamic law, which forbids both the payment and receipt of interest. Rather than lending money to a customer to buy a property, the bank buys a home for the customer, who then pays the purchase price in monthly instalments.
As the bank is the legal owner of the home, the customer also pays a monthly rent, which decreases as the customer buys the bank's share of the property. Eventually the customer buys out the bank, at which point ownership is transferred."
I don't know how much the 'rent' would be, but perhaps not such a good idea after all. Playing with words to comply with mediaeval beliefs!