Official data published by NHS Digital earlier this year showed a headcount figure of 41,985 GPs in England based on data collected on 31 March 2016.
This translates into an FTE GP workforce of 34,914, the data show.
But senior GPs are concerned that the way this FTE figure is calculated misrepresents the true scale of the workforce available to general practice, at a time when accurate data on a profession in crisis is vital.
NHS Digital collects data on the number of hours GPs work at all practices that submit data through a system called the Primary Care Web Tool - and with more than 7,000 practices responding (92.7% of practices in England) in March 2016, the figures offer an accurate snapshot of the in-hours primary care workforce.
GPs in England complete just over 1.3m working hours a week, the data show. NHS Digital translates this figure into an FTE GP workforce figure by dividing it by 37.5 hours - the standard working week - to give 34,914.
Under the current system, an individual GP working 75 hours a week counts as two FTE GPs. Two FTE is the maximum an individual GP can be counted as in the FTE statistics, so any GP working more than this would still count as just two FTE.
Under a method used until 2015, the maximum FTE for a single GP was capped at 1.28, but this was changed because large numbers of GPs worked more than the 1.28 FTE statistical cap, meaning their full contribution was not properly measured in the published data.
But some GPs say the new system is effectively 'double counting' GPs, because around a third of GPs overall - excluding registrars, retainers and locums - and around 44% of partners counted as more than one FTE.
GP working hours
GPC workforce, education and training subcommittee chair Dr Krishna Kasaraneni says NHS Digital should publish simply national and regional headcount figures, and the total number of hours or days worked by these GPs.
'Converting it into an FTE figure is arbitrary,' he said. 'There isn't really a standard definition of what one FTE GP is - wherever you draw the line doesn't make sense. I know GPs who work three days a week and work easily 37.5 hours.
'And if a full-time GP works nine sessions - I don't know many who do that in a 37.5-hour week. This is essentially double counting.'
Dr Kasaraneni pointed out that with GPs working longer hours because the profession is under rising pressure, the figures would suggest that the workforce is growing while GPs are simply working harder.
He added that the figures should also find a way to factor in how much the doctors counted worked for out-of-hours services.
Analytical section head at NHS Digital Ian Thornber told GPonline that his organisation was open to looking at different ways to present the data.
'The data are currently classed as experimental. If the GPC would like them presented in an "hours" format, I’m sure we could look at that. We have been communicating with the BMA.'
He said the main piece of feedback that had come from NHS organisations was a demand for GP workforce data calculated at the level of each of the 44 sustainability and transformation plan (STP) areas in England.
Mr Thornber added that NHS Digital was looking at different ways to present the information gathered from practices. One option was to present data on the percentage of GPs in each area working within different ranges of hours per week.
He said the organisation worked carefully to 'de-dupe' data to prevent GPs being counted multiple times in data from different organisations, and cross-checked information by 'triangulation' against a range of other data sources.