Sunderland offers buy-to-let investors the biggest returns of all major university towns and cities in the country, according to LendInvest, an online mortgage lender. The north east city has averaged a rental yield of 6.5% in 2016, putting it top of the table.

In second place was Manchester at 6.2% and third Liverpool at 5.5%.

Only one postcode area of London makes it into the top 20. Rental yield in East London was 4.6%, putting it 19th.

"Student towns are an excellent option for investors; there's a steady stream of demand with each new academic year delivering prospective tenants," said Christian Faes, co-founder and chief executive of LendInvest, which based its research on data from the Land Registry and Zoopla..

"With A-Level results out today and the year's clearing for university places swinging into action, where's best for student lets will be on the minds of many landlords.

"However landlords need to look beyond simply how big the local student population is. For instance, there are many thousands of students attending universities in London, yet when it comes to rental yields there are far more profitable areas to invest in than the capital."

Buy-to-let investors have been the target of a number of tax increases by the Treasury. Buyers of additional property must pay a 3% surcharge on top of the basic rates of stamp duty. Moreover, tax reliefs for mortgage interest payments and maintenance costs have been cut.