NASGP chief executive Dr Richard Fieldhouse said locums are not attached to any one practice but may have worked in many, or even all, the practices in a consortium.
'Your commitment will be to your consortia, while GP partners first priority will be their practice,' he told GP's locum conference in London, last week.
But Dr Fieldhouse warned that, as practices form tighter consortia, they will start hiring locums through agencies.
'I think, with consortia, the next five years for locums will be very different,' he said. 'Consortia will be more likely to use agencies to get a better deal across practices and less likely to deal with individuals.
'If a practice has an issue with you and therefore the consortia decides it doesn't want to work with you, you're stuffed.'
He said that, although many GPs working in high-profile management positions work as locums, there was little evidence PCTs are engaging young locums to join consortia.
'Many GPs that have worked their way up consortia or PCTs are ex-partners that have become locums so they can spend more time in the role.
'But PCTs are missing a trick if they fail to reach out to get younger locums involved in GP commission,' he said. 'Much of the White Paper consultation seems to have gone over our heads as locums.'