Alrayan Bank formaly known as Islamic Bank of Britain who provides Islamic Mortgage

I live in UK and want to buy a house in a year's time. There is only one bank in UK Alrayan Bank formaly known as Islamic Bank of Britain who provides Islamic Mortgage. I want to know mortgages provided by them to buy a house in UK are halal. Their website says various Muftis names including Molana Mufti Taqqi Usmani.

Important Point: When we purchase house through Alrayan Bank they will charge me rent every month which is not based on the rent in the area however it will be based on Bank of England's interest rate. If interest rate is 2.99% Alrayan bank will charge 3.99% (% are just used as an example).

So the confusion here is even the bank call's it rent but it's still calculated on the bases of interest rate.

Secondly, I heard from friends and other people that some Mufti's say that we can buy a house on normal mortgate (means interest mortgage) if we are not doing any business with it like renting a property or using it for business purpose.

I hope you understand my question and will be able to help at your earliest.