Figures published by NHS Digital last month show that there were around 3.1m ghost patients in England in 2017 compared with around 2.2m a decade earlier.
Over the same period, numbers of ghost patients in Wales fell from around 88,000 to 81,000, while in Scotland the figure was almost unchanged at around 274,000, and Northern Ireland saw a rise from 71,000 to 99,000.
The figures reveal that 'ghost patients' - which represent the gap between the number of patients registered at GP practices and the estimated population - have risen sharply since 2015, when the outsourcing company Capita took over responsibility for Primary Care Support England (PCSE).
GPC chair Dr Richard Vautrey said: 'I don't know why there may be more [ghost patients] but it could be linked to the rise in the overall population of the country and/or greater mobility of patients within the country.'
He said the change 'could also be related to the way PCSE is managing the registration process' but that he had 'no evidence either way' to demonstrate whether this was the case.
Capita chose not to comment on the rise in ghost patients in England. NHS England said the National Audit Office and House of Commons public accounts committee had called for regular action to update patient lists, that this work was ongoing with Capita and that all savings would be reinvested into GP services.
Dr Vautrey warned that any future 'list-cleaning' initiatives must be carried out with caution. 'There will always be a discrepancy between the two figures and it's important to ensure any list cleaning exercise is done carefully, is proportionate and does not add unnecessary workload on to already pressured practices.'
Overzealous list cleaning drives by primary care organisations in the past have led to legitimate patients being forced to re-register with their GPs.
A 2005 study in the journal Family Practice warned that 'list inflation is an inevitable consequence of a capitation-based system of funding primary care'.
The study said some patients on GP lists 'probably no longer exist because of death, emigration or moving house', but added that part of the discrepancy arose from people who did exist, but who did not complete the national census - potentially because they were homeless or refugees.
The huge population shifts generated by students moving away from home to university have also been linked to driving up numbers of ghost patients.