The government’s much-lauded efforts to restrict access to online pornography appear to be having little effect, an investigation has found.

From the UK’s four largest internet service providers (ISPs), only 4% of Virgin Media customers agreed to "family friendly network level filtering" when offered the option, whereas 5% of BT customers and 8% of BSkyB consumer have the restrictions activated when prompted on their broadband service.

TalkTalk customers proved to be the most moral, with 36% of customers putting the blocks in place.

The findings come from the second in a series of three reports commissioned by the government from industry watchdog Ofcom to monitor the progress of proposals to limit underage access to potential unsuitable material.

This follows an agreement between the Government and ISPs announced in July 2013, in which the latter committed to offer new customers ‘family-friendly network-level filtering’ by the end of December 2013.

Some networks have been faster than other in implementing the blocks, however, as while BT and Sky launched filter services towards the end of 2013, TalkTalk’s HomeSafe option had been in place since May 2011.

Virgin Media launched its filter, Web Safe, in February 2014, past the deadline set by the UK Government, and the Ofcom study found that the company was only offering the service to 35% of its customers, meaning the number signing up was far lower than the other ISPs.

The report blamed "a failure in process" by Virgin Media for this error, saying that the mistakes happened primarily as a result of actions taken by the company’s installation engineers.

"The majority of new Virgin Media installations involve an engineer visit. Virgin Media believes that in many cases the engineer runs the broadband activation process and bypasses or ignores the filtering choice," Ofcom said.

Responding to this, Tom Mockridge, Virgin Media’s chief executive, admitted the company had "fallen short" in meeting its original commitments.

"We take our responsibility to help families stay safe online very seriously and have taken immediate action to improve how we meet our commitments to government," he said.