More than 40 per cent of customers of these ISPs, when polled by Point Topic, said that they are 'very' or 'fairly' likely to change supplier soon.
According to the research, 12 per cent of UK businesses have changed ISP in the past six months, and 23 per cent are 'very' or 'fairly' likely to do so in the next six months.
"This is broadly in line with our findings last year," said Dr Katja Mueller, research director at Point Topic. "There is some shift from 'very' to 'fairly' likely, but overall it is pretty steady."
Point Topic found that the reasons for picking (or sticking with) a particular ISP have changed over the past 12 months.
While 'service reliability' remains the top concern for businesses, 'price' has slipped down the list when companies confirm what they regard as 'very important' in selecting an ISP.
This contrasts with the selection of fixed telephony supplier, where an uninterrupted service is taken for granted, and 'competitive pricing' was specified as the most important factor by 55 per cent of respondents, against 42 per cent for 'reliability'.
"We believe this reflects the fact that more and more businesses are relying on the internet for business-critical services and applications," said Mueller.
"If the people in your office cannot get their email, or if your warehouse cannot access the stock control system, your business suffers financially.
"Increasingly companies recognise this and are prepared to pay for services that ensure continuity and offer a level of guarantee when something does go wrong.
"Particularly someone to talk to about the problem and the feeling that the ISP has heard them and is doing something about it. It's more of a partnership these days."
Accordingly, the proportion of businesses paying more than £50 a month (but less than £499 a month) for broadband has doubled from 17 per cent in March 2006 to 34 per cent in March 2007.
The research is based on a survey of 1,500 respondents conducted by B2B International and Continental Research in March 2007.
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