Figures for the start of May show that the total number of patients registered with the service has risen to 51,596 - more than 10 times its list size in November 2017, when the service opened up to patients across a wide geographical area.
In November 2017, the GP practice in Fulham, south-west London that hosts the service had a below-average patient list of just 4,970 - making it the 5,074th largest in England.
But from that point, when NHS patients who live or work within 40 minutes of one of the service's five London clinics were allowed to register, its growth has been exponential.
The service has been heavily advertised, with its key feature the offer of rapid online access to a GP - more than 85% of its consultations are delivered remotely, via smartphone or computer.
Babylon GP at Hand describes itself as a 'full NHS GP practice, with no restrictions on which groups of patients can register', and denies claims that it has 'cherry-picked' younger patients.
However, patients attracted to the service have been predominantly young - with 85% of people signed up with the service now aged between 20 and 39 years old. Across the registered patient population of England as a whole, just 28% of patients are aged in this range.
The largest 10-year age band registered with GP at Hand is patients aged 20-29. A total of 26,097 patients in this age group are registered with the service - just over half its total list.
Analysis by GPonline shows that these 26,097 patients account for nearly one in 300 of the entire registered patient population in England in this age group.
One in 400 of all patients in England aged in the 20-year age band from 20-39 years old are signed up with the service.
GP at Hand looks set to continue its rapid growth, adding more than 2,500 patients to its list in all but one of the past seven months. The service has also been given the green light to expand to Birmingham - although details of when this could start have yet to be made public.
Despite the rapid rise in its registered list, patient turnover has also been huge at GP at Hand - GPonline revealed earlier this year that one in four patients who had signed up with the service between November 2017 and March this year had subsequently left.
GP leaders have hit out at the disruptive impact on other practices in and around London that have seen predominantly young patients move to the digital-first provider, stripping out income that effectively subsidises the cost of older patients who attend more frequently. LMC leaders in Hammersmith warned earlier this year that extended hours cuts linked to the high cost of GP at Hand to the local CCG threatened to force the closure of other practices in the area.
GPs have also hit out at delays in publishing an updated CQC report on the service, and a report commissioned by the local CCG.
A Babylon spokesperson said: 'Many of our users joined us because they had an existing healthcare need but were faced with long waiting times or couldn’t make it to their previous GP - by using digital-first consultations these patients can get NHS GP appointments any time, any day, often within two hours of booking and at no extra cost to the NHS.
'Babylon’s mission is to make healthcare accessible and affordable for everyone on the planet, so we are proud that we are making healthcare more accessible for the 50,000 people who have chosen to join our NHS service GP at Hand.'