I also heard about a so-called "interest-only" mortgage, though I'm unable to elaborate on it.
You can get an 'interest only' mortgage if you have some other sort of repayment vehicle to pay off the capital at the end of the mortgage term... something like an endowment, or an ISA, or some other sort of investment.
Say you want to borrow £100,000 on an interest only basis... your payments to the lender would be relatively low, because you are only paying the interest on £100,000.
But at the end of the term, say 25 years, you would still owe the lender the original £100,000 that they loaned you. This is where you would cash in your ISA or endowment, which has to be guaranteed to be worth at least £100,000 so that you can pay off the capital balance you owe the lender.
That's roughly how it works..