As a general rule, most mortgage lenders will not let you borrow more than 85% of the property value, and typically lenders expect the rental income to be around 130% of the mortgage payment you make.
The above rule is only a guide and some lenders will change their standard lending criteria for some investors (such as those with multiple buy to let properties and therefore other sources of income) but the surplus gives an important cushion against ‘voids’ i.e. empty periods where the property is not rented out.
As well as requiring a decent sized deposit (15% or more is often required), you are expected to own your own personal property. It is also worth noting some lenders are unhappy providing buy to let mortgages on ex-council property, flats above a shop or in a high-rise block basically as these types of property add to the risk.
All the major whole of market brokers offer buy to let mortgages and as there is fierce lender competition in the buy to let market, providing you meet the borrowing criteria, you can expect to get a mortgage at or only slightly above residential rates.