GPs were so stunned by the terms offered to them when negotiating their new contract that they thought it was a "bit of a laugh", a doctor has said.
The new contract was introduced in 2004
Dr Simon Fradd, who was one of British Medical Association's GP negotiators, said they were shocked by the approach taken by the government.
They could not believe it when GPs were given the chance not to do evening and weekend work for a 6% pay cut, he said.
Since the deal started in 2004, average GP pay has topped the £100,000 barrier.
While doctors now make less in basic pay - about £55,000 on average - they have been able to top-up their earnings by hitting targets under a performance-related bonus scheme.
Opponents have often criticised the government, claiming they mishandled the contract, which is now contributing to NHS deficits.
Earlier this month, Health Secretary Patricia Hewitt admitted she wished the government had capped the profits doctors could take out of the practices because of the soaring sums.
Dr Fradd was part of the negotiating team representing the British Medical Association during the two years of talks between 2001 and 2003, although he is no longer on the BMA's GP committee.
Interviewed for BBC Radio 4's The Investigation, which will be aired on 1 February, Dr Fradd said doctors had never believed the government would be willing to allow them to opt out of out-of-hours care.
And when they did, he was surprised the NHS Confederation negotiating team, acting on behalf of the government, was only asking for a 6% cut in pay.
He added: "We got rid of it for effectively 6% of the value of the contract. It was just stunning. Nobody in my position had ever believed we could pull it off but to get it for 6% was a bit of a laugh."
Since the contract came in, nine out of 10 practices opted out of providing care.
NHS trusts have put alternative arrangements in place, but hospital A&E departments have reported an increase in patients.
In a separate interview, he told the BBC that he still thought the contract offered good value for money for patients as GPs were still taking up a relatively small part of the NHS budget.
"I think the government underestimated how much out-of-hours care was worth, but there are other parts of the contract, such as performance-related pay, which were harder to sell to doctors."
Looking back on the new contract, NHS Confederation chief executive Gill Morgan said she felt there were too many sweeteners in the deal offered to GPs. "I think it is always easy to underestimate how strongly GPs respond to an incentive that gives them money."
Dr Hamish Meldrum, chairman of the British Medical Association and a member of the BMA negotiating team, would not reveal how much the negotiators would have accepted when it came to the opt out although he said it was "not a sticking point".
"There were areas of the package where big concessions were made. We agreed to other providers in general practice and the other one was performance-related pay."
Health Secretary Patricia Hewitt said: "It is just worth remembering that at the time when that deal was being negotiated several years ago, GPs were retiring early and the new medical students weren't coming in to be GPs.
"Of course, we had to do something about it and we did. And I'm very proud of the fact, and I think that the BMA is as well, that we have got the best GP service in the world."
The Investigation, BBC Radio 4, 2000 GMT, 1 February, 2007.