Plans to force internet service providers (ISPs) to disconnect suspected illegal downloaders have been roundly rejected in a new YouGov poll, the first time public opinion has been tested on the issue.

Nearly 70% of those surveyed said someone suspected of illegal downloading should have a right to a trial in court before restrictions on internet use were imposed. Only 16% were in favour of automatic curbs based on accusations by copyright holders such as musicians, as is proposed by the business department.

ISPs such as TalkTalk and T-Mobile complain that the government's proposals expect them to bear the costs of protecting a third party's rights. They warn that the move will not work because illegal filesharers can avoid detection by encrypting the traffic, or by hijacking someone else's IP address or using their Wi-Fi network.

Ministers have insisted that disconnection is a last option and something on which they are consulting. They are, however, facing a growing backlash, with an all-party motion urging a rethink of the policy on disconnection being led by Tom Watson, the former cabinet office minister responsible for digital inclusion.

Jim Killock, executive director of the Open Rights Group, the organisation that commissioned the YouGov poll, called the government's plans extremist.

"This poll shows people rely on the internet, and an overwhelming majority think that access should only ever be withdrawn as the result of court action.

"Nearly a third would be much less likely to vote for a party that supports disconnection proposals.

"Clearly Lord Mandelson, the business secretary, is out of step with public opinion and should think again."

The poll also found that among younger voters, the threat of internet disconnection for online copyright infringement might be a vote-changing issue.

Meanwhile the Conservative shadow culture secretary told the Financial Times a Tory government would scrap the proposed 50p a month tax on all telephone lines, aimed at raising £150m to £175m a year to support rural broadband projects. Jeremy Hunt said it would be scrapped a "soon as possible" after the general election expected in May. He said the party was also considering reversing government plans to force the BBC to share £130m of the television licence fee with other broadcasters.

The poll found a third of UK citizens (31 %) would be much less likely to vote for a party that supported internet disconnection for infringements.

A further 13% would be a "little less likely" to vote for that party: in total, 44% would be less likely to vote for a party that supported such a policy.

Nearly three quarters (73%) said if they were disconnected, they would find their ability to use vital commercial services, such as shopping and banking, completely disrupted or fairly harmed.

When asked to choose, respondents also supported the right to a trial before punishments are imposed.

A total of 68% of respondents said that, if the Government's proposals go ahead, a court should consider the evidence before restrictions were imposed, while only 16% were in favour of automatic procedures based on accusations, as is currently proposed.

An inquiry into the issue by the all-party parliamentary communications group concluded last week that "much of the problem with illegal sharing of copyrighted material has been caused by the rightsholders, and the music industry in particular, being far too slow in getting their act together and making popular legal alternatives available".

It added: "We do not believe that disconnecting end users is in the slightest bit consistent with policies that attempt to promote eGovernment, and we recommend that this approach to dealing with illegal filesharing should not be further considered."

The commons motion tabled by Watson and others calls for users to be given the right to go to court before seeing their access to the internet is ended.

Sion Simon, the minister for the internet, insists the government will not allow arbitrary disconnection.

In an article in the Birmingham Post he explained: "As a first step, where rightsholders identify unlawful activity, ISPs will be obliged to notify accountholders that their account appears to have been used to infringe copyright.

"The infringer (who may, for instance, be a child) is very often not the accountholder (perhaps a parent), who will often be quite unaware of what is happening. For many people, a letter will be all it needs to put an instant stop to the offences.

"ISPs would also be obliged to keep anonymised records of the number of times individual subscribers are identified breaking the law.

"On production of a court order, that data could be used in targeted court action by rightsholders against those responsible for the most damaging breaches of copyright."

He has stressed that only as a last resort government could require "Ofcom to demand that ISPs take technical measures against those people who repeatedly ignore the law. That could mean capping the broadband speed or filesize someone can access".