Between April 2013 and October 2014, practices in the Cambridgeshire and Peterborough CCG area saw an increase of 25,789 registered patients - 239 more per practice.
Over the same period, Health and Social Care Information Centre data show the number of registered patients at practices in Tower Hamlets, east London, rose by 17,584.
The surge added an average 488 patients per practice in the area and represented a 6.4% increase in the area's total patient population.
An increase of 12,142 patients during that period in Brent, north-west London, added 181 patients per practice, and a rise of 7,845 patients across Dartford, Gravesham and Swanley CCG in Kent boosted average lists by 231 patients.
Milton Keynes CCG saw practices register an extra 7,055 patients in 18 months, an increase of 2.6% in the patient population.
Other CCGs that saw significant increases include North Manchester, Newcastle North and East, Bedfordshire, Sandwell and West Birmingham, and Nottingham City.
Londonwide LMCs medical director Dr Tony Grewal said he was unaware of the huge rise in patient numbers and no extra help for practices had been provided.
He called for a one-off 'registration' payment to help practices dealing with such a large increase in patient numbers.
'Recent research suggests that in London, the average patient will use as much practice resource in their first year after registering as for the whole of the rest of their time registered with that practice,' he said.
One-off payment needed
'It would make sense for this to be recognised, ideally as a new patient registration payment.'
Kent LMC medical secretary Dr Michael Parks, who represents GPs in Dartford, Gravesham and Swanley, said rapid growth in the area was fuelling pressure on GPs.
'It's likely to accelerate and that may become a problem for health services locally in the future, and not just primary care,' he said. GPs were considering closing lists and there were the 'usual problems' with recruitment and retention, he added.
'Practices would normally see an increase in their list size as a positive, but I'm not sure they would in the current circumstances,' he said.
'There are no local schemes, perhaps there should be.'
GPC deputy chairman Dr Richard Vautrey said more core funding must be made available to help general practice cope.
'We have a growing population across the country, but the relative NHS funding for general practice has been cut, rather than increased, so it's no surprise practices are under so much strain,' he said.
'We need urgent funding put into global sum and PMS baselines, which have been frozen for far too long, to pay for core general practice to meet the needs of the growing population, rather than prioritising other schemes, as we've seen with the Challenge Fund.'
Case study: Milton Keynes CCG
Milton Keynes CCG chairwoman Dr Nicola Smith said rapid population growth in Milton Keynes was behind the area's 2.6% patient population increase over the past 18 months. The CCG was working with NHS England to find 'solutions' for practices, but the rise in numbers was only likely to continue, she added.
'We are supporting individual practices that are experiencing difficulties by sharing good practice from those surgeries that are performing well, such as better use of telephone consultations or changing skill mix to make better use of other staff, such as practice nurses,' Dr Smith said.
A spokesman for NHS England's Kent and Medway area team said it was 'keenly aware' of the challenges facing local GP practices.
'We are working with CCGs and practices to identify how practices can work across local networks in order to be sustainable while delivering excellent care that drives improved outcomes for patients and communities,' he said.