On 1 September 2020, GP at Hand had 84,140 registered patients - second only in size to the Octagon Medical Practice, which serves 84,794 patients in the Cambridgeshire and Peterborough CCG area.
But Octagon - formed after a merger of eight practices in 2017 - has announced plans to break up into smaller groups from April 2021 to fit better with primary care networks.
The move will leave GP at Hand - the controversial digital first NHS service run by private company Babylon - with the largest patient list in England.
Digital first GP service
However, its rapid growth could see the service overtake Octagon well before its planned break-up - potentially as soon as this month.
The creation of GP at Hand has transformed a small west London GP practice - which in November 2017 had less than 5,000 patients - into an organisation with nearly 85,000 registered patients who live across a wide geographical area.
The service promises promises rapid access to predominantly video consultations, but patients can also see a GP at one of about half a dozen physical locations in London. From last year the service also operates from Birmingham, and plans to open soon in Manchester.
GP at Hand's growth has slowed during the COVID-19 pandemic - but its registered list continues to rise, and figures due to be released later this month could show it already has the largest list in the country.
Patient list size
The growth of GP at Hand's patient list could be stopped - or at least masked - under NHS England's plans to break up lists held by digital first providers. Last year, NHS officials set out plans to force digital first providers to set up a new physical GP practices with a separate registered list in any CCG area from which they register more than 1,000 patients.
As of September last year, this looked set to mean GP at Hand would have to be broken up into around 17 separate patient lists, potentially from April 2020.
The move has yet to take place however, and the BMA called this month for it to be halted to avoid distracting local NHS systems coping with extreme pressure through the second wave of the COVID-19 pandemic.
Although average GP patient list size has been rising fast over the 15 years since the practice-based 2004 GP contract took effect - a change that has accelerated in the past seven years since NHS England was established - the average patient list in England is just over 9,000 patients.
GP at Hand's list is more than nine times above the average size - and the service is among a group of just 11 practices with more than 50,000 patients on a single practice list.
However, this does not take account of practices working together or cases where a single provider operates multiple contracts. Octagon, for example, currently manages a further eight practices on top of the eight that merged to form its main 84,140-patient list.