Comparison website uSwitch – now owned by property portal Zoopla – has hit out at landlords and agents who allegedly deny tenants the right to switch energy suppliers.

The new accusation comes despite a high-profile BBC Watchdog investigation in 2013.

The BBC then named Reeds Rains, Your Move and Foxtons as having links with Spark Energy. All the firms vehemently denied any wrongdoing.

uSwitch has now opened fire again, and said that 13% of landlords are denying tenants the right to switch, with 19% of landlords with three or more properties preventing a switch.

uSwitch says 36% of landlords wrongly believe that by naming a preferred supplier in rental agreements, they can stop tenants switching.

Research earlier this month was conducted among 500 landlords and 1,000 tenants.

Based on this, uSwitch calculates that 230,000 tenants who have not switched say it is because their tenancy agreement forbids it.

uSwitch is now calling on the Competition and Markets Authority to insist that all tenancy agreements should state that tenants who pay for their energy directly have the right to switch suppliers.

It is also calling on letting agents and landlords to drop unfair clauses in tenancy agreements, and to inform tenants at the start of each tenancy about how to switch.