However Hall said that these losses are now reducing as the effects of lower mortgage and deposit rates and as modest rises in property prices filter through.
Hall said: “There is a scale of risks with cash buyers with a single property at one end and highly geared interest only investors with portfolios of many properties at the other.
“The latter group makes the bigger returns when times are good but it is hit the hardest if markets fall or rates rise.
“We are now moving into unchartered waters where past performance may not be a definitive guide to future returns.”
Hall made the claims as TMW publishes its latest buy-to-let profitability figures. TMW found that average buy-to-let rate has now fallen to 4.28% from 5.09% in August 2012.
Estate agents say confidence is soaring and property prices are expected to rise. Buy-to-let lenders report rising optimism, distributors report high levels of remortgaging (as landlords release funds to expand their portfolios) and brokers confirm that buy-to-let is surging.
Finally estate agents report that tenant demand continues to rise, as government initiatives to resolve exclusion from homeownership are mire down by disinterest and criticism.
However TMW warned that properties buy-to-let investors buy today remain overpriced and the potential exists for a correction.
Hall said: “Buy-to-let is a long-term investment and there is a risk that landlords could become complacent and over-dependent.”
TMW has published a beta version of a Review Model on its website to help prospective buy-to-let investors evaluate the potential returns for themselves.