You are right, these types of flats often fall outside of mainstream buy to let lending criteria; however, there are specialist lenders that will look at this type of investment. These lenders can only be accessed via intermediaries so make sure you talk through the options with a broker.
The value of the property and the location will be important factors. Any lender will need to be assured that the flats are in an area popular with renters. This information will be addressed in the valuation report. As with any buy to let investment the lender will also want to see rental income of at least 125-130 per cent of the mortgage interest pay rate. Assuming that these factors stack up you can expect to borrow up to 75 per cent of the value of the property. You will also need to ensure that you have a clean credit history.
1st January 0001