The website has set up dozens of 084 numbers which charge up to 52p a minute to ring when free ones are available.
The calls connect through to insurance companies, even though many have their own free or standard rate lines.
It means a customer could pay as much as £3.60 if they spent 20 minutes on a landline phone to an insurer, or £10.40 if they were calling from a mobile.
The Sun obtained 26 online car insurance quotes from Go Compare.
Just one gave the insurer’s own free number but the others were all expensive 0843 codes with no mention of cheaper alternatives.
From a landline these would cost up to 18p a minute to ring – including the 7p a minute service charge and an access charge which could be as high as 11p a minute. The access charge goes to the caller’s telephone provider.
But to call from a mobile, the costs could soar to as much as 45p a minute for the access charge as well as the 7p a minute service charge amounting to up to 52p a minute.
Craig Sellars, 47, was charged £22.59 for a 52-minute call on his mobile to insurer Swinton about his building insurance.
The operations manager, from Nottingham, said: “When I checked my phone bill I couldn’t believe it.
“The thing that really got my back up was I went on the Swinton website later and saw an 0800 freephone number which I could have used.
“It’s not very customer focused is it? It’s cheeky. It’s not very transparent that they are going to make any money at all. It’s underhand. In the short term I have a much larger monthly bill than I would usually.
“They need to change from 0843 numbers to freephone numbers.”
David Hickson, of the Fair Telecoms Campaign, said: “What Go Compare is doing, imposing a service charge through the use of indirect 0843 telephone numbers, is quite simply a rip off.
“It contradicts Go Compare’s bold claim that it does not charge people for using its services which it clearly does in this case.”
Calls to 0800 numbers are free from any phone and calls to 01, 02, and 03 numbers are normally made at no cost to the caller.
Last night a spokesman for Go Compare said the site was soon to discontinue its use of 0843 numbers.
He said: “Our customers have always been able to use our website for free to compare prices and product features, and clicking through to complete a purchase has never carried a charge.
“As part of our ongoing commitment to improving our customers’ experience, we are currently in the process of changing all 0843 numbers to 03 prefixes, and we expect this update to be completed by the end of July.”
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