Kristjan Byfield, director of sales and letting agents at Property Specialists, a London-based agent, said: "In much of the country, buy-to-let has become the engine room of the property market as a whole. Low interest rates have achieved a neat double act - making mortgages more affordable, and making buy-to-let a substantially more attractive investment than low-paying savings accounts. Average net rental yields for buy-to-let landlords in London are currently between 6% and 10% - not to mention the potential capital gains property can offer. Given the paltry levels of interest paid to savers, buy-to-let has an irresistible financial logic for a growing number of people who have some money to invest. A proposed European Directive this year, however, could affect the market. Buy-to-let loans, which are treated as commercial loans and therefore outside of the mortgage remit of the Financial Services Authority, could become regulated. The CML's Mr Smee said: "If this does happen, policymakers must ensure that the very clear differences between buy-to-let and owner-occupier lending risks and operations are fully recognised in any regulatory framework that may emerge."