Virgin, BT, Sky and TalkTalk's porn filters are being used by less than one in seven households, Ofcom has reported.
The four main ISPs, Ofcom and the government discussed the plans last year, requesting all four providers installed such filters with a deadline of December 2013.
Virgin Media was the last to install the filter, which was completed in February. It says only four per cent of its new customers are using the tool, which is much lower than TalkTalk customers, where it is thought 36 per cent of customers are doing so.
TalkTalk had previously been using its HomeSafe tools that also protect children and families from harmful websites, just like the porn filter, so it's no surprise uptake was so high. BT said five per cent of its customers were using its tools, while eight per cent of Sky users had opted in to block porn websites.
The report revealed that Virgin Media was only offering the service to 35 per cent of its customers, while the three other ISPs offered every new customer the tools.
Ofcom said: "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. It has recognised that this is a failure in process and indicated it is taking steps to address this gap.""
Virgin Media's chief executive, Tom Mockridge, responded to the report saying: "Ofcom's report clearly highlighted where Virgin Media has fallen short in meeting our 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."
