Small GP consortia should form 'federations' to manage financial risk, according to guidance from the GPC.
In GP Consortia Commissioning: Initial Observations, published last week, the GPC says consortia size should not be prescribed.
But the report says large consortia will find it easier to 'engage in credible interaction with acute care trusts' and to attract high calibre leaders.
It adds that consortia covering populations of less than 500,000 will struggle to manage financial risk.
Consortia are likely to cover populations of between 100,000 and 750,000, the report says, and those at the bottom of this range should federate with neighbouring groups.
Federations of consortia could share services, pool financial risk and benefit from economies of scale, it adds.
The GPC also wants to avoid early adopters or small practice-based commissioning groups becoming consortia leaders without the support of all local practices.
Practices in a locality should elect a 'board of appointments' to recruit clinical leaders for consortia, the report says.
But National Association of Primary Care (NAPC) president Dr James Kingsland said it was 'premature' to try to establish the structure of consortia.
He said there was no evidence for the GPC view that consortia would cover between 100,000 and 750,000 patients.
'I've seen some fantastic developments covering as little as 40,000 or 50,000 patients. Why suggest to them that it is going to be 100,000 when they have been successful?'
Smaller consortia may have to pool risk, he said, but they would be 'more reactive and flexible to local needs'.
GPC deputy chairman Dr Richard Vautrey admitted the guidance was likely to change. He warned: 'Arrangements GPs put in place should be flexible to deal with changes.'
The GPC report assures GPs that good commissioning will bring a 'more rewarding' and 'less complex' working life as outcomes and services improve. The guidance also urges consortia to hold public meetings to help patients engage with them.