Houses without broadband could be worth as much as 20% less than comparable properties with a good connection, according to experts who say superfast speeds are increasingly important to prospective homebuyers.

With soaring numbers going online to perform everyday tasks or to work from home, a robust connection is considered so vital that the property search website Rightmove has added a broadband speed checker button to every one of its listings, alongside details of transport links and schools. Estate agents report that rising numbers of buyers are willing to pull out of a deal if broadband is not available in that area.

Bernard Phillips, the head of consumer platforms at Rightmove, said: "We already offer a number of tools to help consumers make informed decisions about a property, and we're pleased to be the first to add broadband speeds to this. Broadband has become ingrained in people's lives and is an important factor when choosing a home."

Yet many households – particularly those in rural and hard-to-reach areas of the UK – remain stuck on sluggish speeds of 2Mbps (megabits per second) or less. That can make anything aside from sending and receiving emails a struggle. The government's rollout of the superfast network to reach 95% of the UK, promising downloads at more than 30Mbps, has been pushed back to 2017. The latest figures from the communications regulator, Ofcom, show that 73% of the country is currently able to access these speeds.

This is despite the fact that broadband is now regarded as "the fourth utility" after gas, water and electricity, according to property expert Henry Pryor. "A home without at least a standard broadband connection could be worth up to 20% less than a comparable property," said Pryor. "The more demanding buyers now want fibre-optic superfast speeds as, whether working from home, streaming entertainment or managing the stack of equipment that now relies on this, a property needs to have 21st-century connectivity."

Gillian Guy, chief executive of Citizens Advice, which has seen a 27% rise in the number of people seeking help over broadband and internet issues since April last year, said: "A poor internet service can shut people out of contributing to the national economy, and people living in rural areas can find unreliable internet a particular struggle."

Frank Speir of property buying agency Prime Purchase said: "Seven or eight years ago, the issue of broadband speeds was never brought up by clients. Six years ago they started mentioning them as something nice to have, and now it is absolutely fundamental to many buyers that they have fast broadband."

One client buying in a small hamlet of four houses just outside Oxford went so far as to club together with neighbours to lay four miles of cable to get high-speed broadband, he added. "It cost them £50,000 each, but they considered it worth it, as it enabled them to work from home and would also make the properties far more attractive to buyers in the future."

Charles Birtles, a buying agent working in Wiltshire and Hampshire, said: "Recently I had a client who was moving from London to Hampshire and a condition of the sale was internet speed. Unless the seller could prove that his home has access to high-speed internet, he would not proceed with the purchase."

This follows news that Ofcom is consulting on performance targets that BT Openreach must meet – or face possible fines. Openreach, which manages access to the UK's copper telephone network that underpins almost every broadband connection, has been heavily criticised by customers for being mismanaged and understaffed. Thousands of households have complained that they face waiting weeks or months to be connected to broadband.

Ofcom stipulated that from next month Openreach will have to repair around 67% of reported faults within two working days. It will also have to provide an appointment for around 54% of new line installations within 12 working days. By April 2016, 80% of problems will have to be dealt with within those time constraints.

• This article was amended on Sunday 2 March 2014. Ofcom figures show that 73% of the country is currently able to access download speeds of more than 30Mbps, not 19% as we said. This has been corrected.

• This article was further amended on 18 March 2014 to correctly identify Charles Birtles as a buying agent, not an estate agent.