Between November 2017 and January 2019 a total of 55,556 joined the digital first provider, according to figures obtained by GPonline under the Freedom of Information Act.
Over the same period 15,623 patients deregistered from the service - more than one in four of the total number who signed up.
GP leaders said the rapid turnover of patients was 'concerning' and warned that it would leave the NHS facing 'significant increased costs'. Finance papers published earlier this month by Hammersmith and Fulham CCG revealed that a £10m hole in its finances triggered by GP at Hand could threaten other services in the area.
Babylon GP at Hand admitted that the figures reflected the fact that many people signing up for the service were unaware that doing so meant they would be deregistered from their existing GP practice.
November 2017 marks the point at which the digital first provider began to grow its patient list exponentially using out-of-area patient registration rules to attract patients living and working across a wide area in and around London.
The latest official figures show that Babylon GP at Hand now has 46,230 patients in total - almost 10 times the number on its books in November 2017. More than half of patients registered with the service are aged 20-29 and 85% are aged 20-39 - sparking accusations of 'cherry picking', which Babylon GP at Hand denies.
GPC chair Dr Richard Vautrey told GPonline: This extremely rapid turnover is concerning but not in the least surprising. People are obviously predominantly using this service as they would NHS 111, for immediate and short-term care rather than long-term continuity of care.
'Not surprisingly patients won't understand the NHS funding consequences of this pattern of behaviour, with the significant increased costs to the NHS compared with routine GP services. To provide this to all patients would rapidly bankrupt the NHS which is why urgent steps need to be taken to reform the out-of-area registration arrangements, something I'll be calling again for in my LMC conference speech.'
A spokesperson for Babylon GP at Hand told GPonline: 'We now see far fewer people de-registering from Babylon GP at Hand. We believe the figures you cite are a legacy from the launch of Babylon GP at Hand when many people did not realise they would have to de-register from their existing practice.
'We greatly improved how clear we are regarding registration and new users are fully aware that, just as with any joining any new NHS GP practice, they must de-register from their existing practice first as they can only be registered with one.'
GPonline reported earlier this month that GPs had raised the alarm over the CQC's failure to update its rating of GP at Hand to reflect the digital element of the service.
Dr Vautrey will highlight ongoing talks over GP contract changes to reduce funding for digital first providers and limit 'abuse of the out-of-area regulations' in his keynote speech at the UK LMCs conference 2019 in Belfast on Tuesday.