Back in April 2017, the Lillie Road Medical Centre in Fulham, south-west London was among England's smallest practices. It had 2,500 patients - a third of the average GP practice list in England at the time.
Since the end of 2016, however, in addition to standard face-to-face appointments the practice had been offering patients access to a digital service using technology and staff provided by private healthcare provider Babylon.
The service provided a smartphone app that allowed patients to access video consultations within an hour, or a response to text messages 'within minutes' from Babylon doctors and nurses. The service - open to anyone within 45 minutes of Lillie Road by public transport - also offered video replays of consultations and an online symptom checking tool.
How fast has GP at Hand grown?
By November 2017, the practice list size had doubled to just under 5,000 patients. NHS England then gave the green light for the service to register patients across a far wider geographical area - sparking an exponential rise in patient numbers in the 12 months to November this year.
The latest figures from NHS Digital show that 36,489 patients have now signed up to the service, which has been formally renamed Babylon GP at Hand. Hammersmith and Fulham CCG has predicted a fresh surge to come in registrations after an advertising campaign launched by the service last month.
Who are the patients signing up with GP at Hand?
Since November 2017, patients across a wide swathe of London and beyond have been able to register with GP at Hand. The service is available to anyone working in zones 1-3 in central London, or living within 30-40 minutes' travel of Lillie Road or one of four further clinics around London linked to GP at Hand.
Around one in 10 of the current practice list lives within the Hammersmith and Fulham CCG area. A further 15% of patients live within the North West London collaboration of CCGs - an eight-CCG group of which Hammersmith and Fulham is a member. The CCG says 68% of patients are from 'other parts of London', while 5% are from outside the London area.
The age profile of the practice list has been transformed - with a huge surge in young patients prompting accusations of 'cherry picking', which GP at Hand denies. In April 2017, 16% of patients at Lillie Road were aged between 20 and 29 years old - by November 2018 this had surged to 49%.
Of the 31,519 new patients who have signed up with GP at Hand over the past 12 months, 87% are aged between 20 and 39 years old.
Patients over 65 now make up just 1% of the population registered with the service - compared with around 10% in April 2017. A Hammersmith and Fulham CCG report in October 2017 predicted that 'patients are likely to self-select in a way that results in a younger, healthier, more mobile population registering for the new service'.
The graph below shows how accurate this prediction has proved, with the practice population shifting from a balanced mix in early 2017 to a model hugely tipped towards younger patients now.
The animated graph below offers a look at how the numbers of patients have changed in different age groups between November 2017 and November 2018 - with an extra 16,360 patients aged between 20-29 years old joining (a rise of more than 1000%) compared with fewer than 200 new patients in total aged over 70.
Why has GP at Hand been criticised?
GP leaders have warned that the funding model for general practice risks being undermined by the GP at Hand model.
As predominantly young, fit patients quit their existing GP practice to join GP at Hand, the practices they leave behind are losing out on a vital source of funding that effectively subsidises the cost of looking after older, more complex patients.
Health secretary Matt Hancock is among the chief cheerleaders for the service - having signed up as a patient with GP at Hand, and declaring soon after taking on the health brief that he wanted services like GP at Hand available across England.
However, the health secretary has acknowledged that the GP funding model may have to change to accommodate GP at Hand - admitting last month that he understood concerns that the service risks creating a two-tier health system that creams off rich, healthy patients and leaves other practices with the poor and the sick.
Hammersmith and Fulham CCG reported earlier this year that it needed an £18m bailout from NHS England to cope with the cost of large numbers of out-of-area patients registering with GP at Hand.
Senior GPs have also warned that offering increasingly rapid access to consultations and advice from GPs may simply drive up demand.
GP at Hand has also been criticised for limiting access to some patients, although a list of restrictions on who can register is set to be removed from the practice's website. Patients 'will still be advised that sometimes it may not be clinically appropriate for them to register with a practice that is not local to their home', however.
For now, NHS England continues to block the expansion of GP at Hand outside of London.