More than 50 MPs have backed calls for urgent improvements to Britain's broadband amid warnings millions of connections may not reach a proposed minimum standard.
The British Infrastructure Group of MPs want automatic compensation for families who do not get the internet speeds they pay for, with Ofcom urged to get tougher on broadband providers.
A new report by the group, titled "Broadbad 2.0", found as many as 6.7 million UK broadband connections may not receive download speeds above the Government's proposed minimum of 10 megabits per second (Mb/s).
Less than half of all UK connections are thought not to receive superfast speeds of 24 Mb/s, according to the group's research.
Ofcom previously found 1.4 million people have download speeds below 10 Mb/s, while the Department for Digital, Culture, Media and Sport (DCMS) said millions of people had not signed up to superfast broadband.
However the MPs say data gathered by Ofcom does not distinguish between connections for customers not signed up to superfast broadband, and those customers not getting the speeds they are paying for.
They argue the current system makes it "almost impossible" to determine how many households do not receive the speeds set out in their contracts.
This is disputed by Ofcom, which said they provide "robust, comprehensive data on broadband take-up and availability".
Former Tory party chairman Grant Shapps, who chairs the group of MPs, said: "Although broadband is increasingly considered to be an essential utility, the quality of customer services has simply not caught up with demand.
"It is unacceptable that there are still no minimum standards in the UK telecoms sector to protect customers from protracted complaints procedures, and ensure that broadband providers are fully accountable to their customers."
Analysis of download speed data recorded by Ofcom in 2015 and 2016 suggested 40.8% of all broadband connections reached speeds above the threshold for superfast broadband.
Figures published by Ofcom in its Connected Nations 2016 report found more than three quarters of premises with standard broadband could get superfast broadband if they upgraded.
The cross-party report, backed by 57 MPs, says it is "unacceptable" Ofcom has not considered automatic compensation for households that consistently get a poor service below what they are paying for.
The MPs want Ofcom to produce better data on the take-up and availability of connections, and consider legal rather than voluntary codes of practice for internet providers.
The report says none of the major broadband providers currently signed up to Ofcom's voluntary code could provide the group with details of their complaints procedures and the amount of compensation they pay to their customers.
Ofcom's voluntary code of practice with providers such as BT and Virgin Media commits them to provide accurate and transparent information on speeds, and allows customers to exit their contract without penalty if speeds fall below a minimum threshold.
An Ofcom spokesman said: "We share concerns that broadband must improve, and we're already taking firm, wide-ranging action to protect customers - including new plans for automatic compensation, faster repairs and installations, and ensuring providers commit to giving accurate speed information to customers.
"We also provide robust, comprehensive data on broadband take-up and availability, through regular reports and interactive consumer tools."
This year's Digital Economy Act set out a so-called universal service obligation across the country, which defined a minimum broadband download speed of 10 Mb/s.
A DCMS spokesman said: "Almost 95% of the UK can now get superfast broadband, but we know millions of homes and businesses have not yet chosen to upgrade.
"We want everyone to have access to fast broadband, and the universal service obligation will make sure that no-one is left behind.
"It's a better offer than any compensation package as it places a legal obligation on providers to deliver the speeds that families and businesses need."