Calls from mobile phones to NHS surgeries using 0844 or 0855 numbers are costing patients a fortune, it emerged today.
An investigation has found patients trying to book an appointment with their GP can be left on hold for 30 minutes and charged as much as £12.
Callers are not warned that they are spending up to 41p a minute from a mobile, while phoning a normal landline number is as little as 2p a minute.
An estimated six million patients across the UK are affected by the scheme which is making huge profits for companies who provide the numbers.
Britain's biggest, Daisy Surgery Line which has contracts with about 1,000 GP practices, made £5.8 million last year on sales of £14 million.
Tycoon Matthew Riley, 39, launched the firm from a garage in 2001. The Sunday Times rich list claims he is worth £85 million.
The probe by the Sunday Mirror tested how long it took for 80 surgeries to answer.The longest was the Dun Cow surgery in south London at 28 minutes and 50 seconds.
This worked out at £11.82 from a mobile charging 41p a minute. A BT landline charging 5p a minute would have cost £1.43.
A wait of 13 minutes and five seconds was recorded for Crawcrook surgery in Gateshead with a cost of £5.36 from a mobile and 65p on a BT landline.
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Put on hold: A call to the Dun Cow surgery in South London took almost 29 minutes and cost almost £12
A call to the Padiham Medical Centre in Burnley, Lancs, was kept on hold for eight minutes and 20 seconds. The bill was £3.41 for a 40p a minute BT landline.
There was no warning to patients calling the 0844 and 0845 numbers of the high cost of the calls if they were using mobile phones.
The investigation recorded that the average wait was one minute and 54 seconds
A spokesman for the Patients' Association told the Sunday Mirror: 'It is morally wrong for GPs to charge patients these rates – many will have no clue. This needs to be stopped.'
Waiting: Patients can pay a big price for using a mobile to contact their surgeries and the logo for the biggest medical phone firm Daisy Surgery Line which has contracts with around 1,000 GP practices
Former Labour Minister John Healey, who won a fight with GPs in his Yorkshire constituency to drop the lines, added: 'No one should be forced to use these rip-off numbers.
'Guidelines created by Labour ruled out this practice. The Government needs to enforce the rules.'
In 2010, the Health Department urged GPs to phase out the premium lines, but many of the medical centres are legally-bound by long-term deals with the telecom providers.
When questioned about the 28-minute wait, the Dun Cow told the paper that the delay was 'definitely not typical.'
A spokesman for Crawcrook blamed the delay on a 'major problem' with its system. It claimed the surgery had installed the 0844 number because patients often found their landline busy.
Waiting time: A call to the Padiham Medical Centre in Burnley was put on hold for eight minutes and 20 seconds costing up to £3.41
A statement from Daisy Surgery Line said: 'It is important to note 084 numbers are not premium rate numbers.
'NHS regulations permit their use provided our GP customers are satisfied that, having regard to the arrangement as a whole, their patients will not be paying more than a local rate call. Surgery Line offers the option of a geographic number.'