Virgin Media is sending letters to the heaviest users of its cable broadband services, highlighting the firm's updated traffic management policies.

Despite continuing to advertise its service as having 'no download limits' the cable broadband provider is placing curbs on its heaviest users by reducing download speeds.

"We are writing to some of our customers to let them know about changes to our traffic management policy," said Virgin Media in a statement.

"As part of this educational exercise we are letting customers know what the changes mean to them, and why they may see their speeds reduced for short periods at certain times of the day."

The company blamed a small percentage of customers for using up "more than their fair share of network resources which affects the service other customers receive".

Virgin Media's move comes hot on the heels of a YouGov survey which showed that more than one in four broadband users are unaware of their service limit, and face being penalised for unwittingly exceeding the limits of their contracts.

The survey, commissioned by ISP PlusNet, also showed that eight out of 10 broadband users have no idea how much of their download allowance they use each month.