GPs in all four countries of the UK said PCOs fail to include them in the routine information cascade to practices.
As a result, they do not hear about new protocols, directives, prescribing guidelines, service updates and local formularies.
A sessional GP in West Sussex said: 'The only communication I ever have is (the PCO's) annual letter about appraisal. Prescribing info? Flu stuff? Education? Commissioning? Conferences? LMC? In my dreams...'
Other locums said PCOs fail to inform them about appraisal.
The Rate Your PCT results confirm National Association of Sessional GPs (NASGP) findings. Only 20 per cent of almost 450 NASGP respondents received information about pandemic flu last year.
'It is a phenomenally poor show if the NHS thinks we do not exist,' said NASGP chief executive Dr Richard Fieldhouse. 'Neither the GPC nor the RCGP has tackled the locum issue.'
He urged the BMA and RCGP to help locums set up groups to share information: 'Locums need to be enabled. It is too hard to do it alone.'
Dr Vicky Weeks, chairman of the BMA's sessional GP subcommittee, said the BMA was addressing these concerns about communication, and had worked with the NASGP.
The Northern Deanery was reviewing how sessional GP groups could be set up, and the subcommittee had worked with LMCs on this, she added.
A spokeswoman for NHS West Sussex said: 'We are not routinely made aware of which GPs provide locum clinics or sessions at practices. Therefore it is difficult to include them directly in our regular communications.'
But Dr Weeks said PCOs should have contact details for 'anyone on your performers list, so you can forward alerts and information'.