Figures from 98 primary care organisations (PCOs) obtained under Freedom of Information rules suggest UK-wide spending on LESs will rise by 3.2% to £318m in 2012/13.
Practices in some PCOs will share LES contracts worth millions of pounds extra this year as commissioners invest in community-based services. In NHS Derbyshire, LES funding will rise by £30,142 per average practice.
But other areas face reductions.
In NHS Cornwall and Isles of Scilly, LES funding will fall £24,610 on average by the end of 2012/13.
Senior GPs warned that even GPs seeing rises in LES funding face increasingly tough targets to earn the money.
In some areas, swings in LES funding can be explained by PCOs rebranding work previously funded under nationally agreed directed enhanced service (DES) deals. But elsewhere, practices will face genuine losses or gains.
Wessex LMC chief executive and GPC member Dr Nigel Watson said small changes to funding could have a huge impact: 'As time has gone on, growth in expenses has outstripped core funding.
'If they take another £20,000 to £30,000 from a practice, that would be catastrophic.'
GPs in England will see a rise of 2.2% in LES funding in 2012/13. But changes vary hugely, with some PCTs commissioning up to £2.8m more than in 2011/12, while others expect to pay out at least £1.7m less.
GPs in Northern Ireland can expect a rise of about 9% in funding once rebranded DESs are discounted. In Scotland, spending will rise by 3.3%.
GPC Wales chairman Dr David Bailey said much of the apparent 19% rise in LES funding predicted by Welsh health boards was due to commissioners 'moving the goalposts' by pushing more cash into LESs from other funding sources.
Dr Bailey warned this would allow boards to negotiate new terms with lower costs and avoid nationally agreed specifications. 'This is going on all over the country. They're not disinvesting in cash terms, but expecting more and more for the same money.'
Many English PCTs have withdrawn swathes of services, including smoking cessation, phlebotomy and LARC fitting. Several said they cut LESs to help meet NHS efficiency savings targets.
Other PCTs have funded new initiatives, such as LESs for in-practice ECG services and care home visits.
GP's investigation also found LESs being withdrawn from practices and offered to private providers. In NHS Darlington, LESs worth £120,000 for IUD fitting and improved access were stopped. Meanwhile, the local cluster, NHS County Durham and Darlington, has invited private providers to bid for a former anticoagulation LES under the any qualified provider scheme.
|Expert view: The accountant|
Laurence Slavin, specialist medical accountant, Ramsay Brown & Partners
'Enhanced services are critical to practices. There's huge variation in terms of what PCTs offer. It mostly depends on the willingness of PCTs to offer them, and they may have financial constraints or local needs. The impact of losing a LES depends on the service and the notice a practice gets. Practices have got to be brave and make difficult decisions if they need to, including about personnel.
'They need to plan, that's the main thing. We've seen practices with dramatic reductions in income. When they are forced to look at their income, they make savings they didn't know they could.'