In 2004/5, partners' average income UK-wide across GMS and PMS was £100,170 - equivalent to £119,271 today in real terms. But data from the Health and Social Care Information Centre show that average income for GMS and PMS partners combined in 2011/12 was just £103,000.
The data show GP income has slumped by 2.1% a year on average in real terms since 2004/5, when the new GP contract took effect.
GP expenses have also continued to rise, with the proportion of gross income now taken up by expenses up 0.7% to 61.6% for 2011/12.
Average income before tax across partners and salaried GPs combined fell 1.2% in 2011/12, official data show, a slight slow-down from the previous year's fall of 1.8%.
Income fell more than twice as quickly among PMS partners than for GMS partners between 2010/11 and 2011/12, the data show.
GMS partners' average income before tax fell 0.7% from £99,000 in 2010/11 to £98,300 in 2011/12, while PMS partners' average income fell 1.6% from £113,400 to £111,600. The average drop across both contracts was 1.1%.
GPC deputy chairman Dr Richard Vautrey told GP that since 2011/12, GP income had continued to decline rapidly in real terms.
He added: 'I think it will get worse before it gets better. GP pay has been slashed, it is no wonder young doctors don't want to be GPs and older ones are retiring as fast as they can.
'Even the prospect of a pay freeze hasn't materialised, since income is falling in real terms.'
Dr Vautrey hit out at the imposed GP contract for 2013/14, which saw the government award a GP funding increase below the amount recommended by the independent Doctors and Dentists Review Body (DDRB).
'The government argued that the award they imposed would mirror hospital doctors' increase, but rising expenses mean it clearly hasn't and won't do. General practice is now among the three least popular subjects young doctors are choosing, along with A&E and psychiatry.
'We will see the crisis in general practice getting worse if the government does not act quickly.'
GP income for partners in England fell faster than in any other part of the UK between 2010/11 and 2011/12, with a 1.5% average drop across GMS and PMS. In Scotland, income fell 0.7%, while Wales and Northern Ireland saw rises in average income of 1% and 5.4% respectively.