GPC leaders in Scotland, England, Wales and Northern Ireland said their preferred option was to retain the UK-wide deal, but that England's reforms put this at risk.
A disintegration of the UK-wide contract would lead to further fragmentation of health services across the four nations, GP leaders said. It could also widen gaps in funding between GPs across the UK.
The 2011 LMCs conference in June voted to maintain a UK-wide deal. But in an exclusive interview GPC Scotland chairman Dr Dean Marshall said the planned NHS reforms in England will make this difficult. He said there were now 'very few similarities' between health policy in England and the three other countries.
'There are differences between Scotland, Northern Ireland and Wales but you could not slide a piece of paper between them. But with England it's a huge gulf,' he said. 'The UK-wide contract cannot continue if politicians continue down their current path.'
'In the next three to five years it is unlikely we will have a UK-wide contract if things continue in the way they are going.'
Dr Marshall said if the UK-wide contract was broken, each country would have its own GP contract by 2016 as a 'Celtic contract' across Scotland, Wales and Northern Ireland 'would not work'.
GPC deputy chairman Dr Richard Vautrey agreed that there was a risk the four-country contract could be undermined by the NHS reforms.
'The risk is not that the other countries move away but that England moves away,' he said.
Dr Vautrey said the GPC would 'work hard to preserve the UK-wide contract and avoid that situation'. The UK deal was 'for the mutual benefit of all GPs in the UK'.
'Without the UK-wide contract there is more potential for yet more fragmentation of health services,' he warned. 'What we need to retain is the sense that patients have the same level of service across the four countries.'
GPC Wales chairman Dr David Bailey said the UK-wide contract could collapse if the plan for a 'quality premium' to reward successful GP commissioners in England was included in the GP contract.
'The GPC is against the plans for a bonus for commissioning performance as it is immoral,' he said. 'If it was written into the GP contract it would create a problem as none of the Celtic nations would want it.'
Northern Ireland GPC chairman Dr Tom Black said Northern Ireland GPs were 'very happy' with the UK deal and would hope to see it continue.
But he agreed that the NHS reforms in England pose a 'significant risk' to the UK-wide contract.
Editor's blog: The under-threat UK-wide contract must continue
