Guidance from the NHS Commissioning Board has set out new principles for “firming up” clinical commissioning group boundaries, and an elaborate formula for resolving disputed areas.

However, even if applied everywhere, the formula still leaves around 8 per cent of the population – or four million people – living in areas not assigned to a CCG, with large gaps in the north of England and West Midlands.

Although CCGs are made up of groups of GP practices, they will also be responsible for a defined geographical area. The precise boundaries have proved difficult to agree as practice catchment areas often overlap.

The guidance has been sent to primary care trusts and obtained by HSJ. It sets out a new principle of “containment”. This states that more than 75 per cent of the population in a CCG’s geographical area must be registered with that CCG’s member practices – and that 75 per cent of the member practices’ patient lists must live within the CCG’s designated area. It also reveals that CCG areas should be built up from “lower super output areas” – defined areas with a population of around 1,500 used by the Office for National Statistics to collect data on local communities.

The board says CCGs should, where possible, avoid a configuration which places member practices in another CCG’s geographical patch.

The document sets out a complex eight-stage formula for deciding which lower super output areas are assigned to each CCG.

If the formula were applied to each of England’s 32,482 lower super output areas, there would still be 2,763 areas – with a total population of 4.1 million – which are not assigned to a CCG.

The formula would not resolve the dispute in situations such as where one CCG is not sufficiently dominant in an area.

The DH guidance leaves small, unresolved areas on most boundaries between CCGs, and large gaps in Staffordshire, the Black Country, Surrey and Yorkshire.

The document offers to make available the results of the exercise where CCGs are struggling with their boundaries.

However, “it would be possible to develop further stages to assign most of the remaining areas… but this would likely require a more manual process and therefore take longer and involve an element of judgement”, it states.

One senior PCT commissioning officer told HSJ: “Practices have been around a lot longer than lower super output areas. If you force this too hard you’re going to start a wave of disengagement, although you nearly had everything sorted. It will cause turbulence where it didn’t exist before.

“It could be like asking a divorced couple to move back in together. You might have two practices in the same village, wanting to be in different CCGs.”

A commissioning board spokeswoman said the document was “a guide, which is not considered to be prescriptive or policy”. She said: “Where CCG areas have been agreed, but are not in accordance with this guidance, CCGs do not necessarily need to start again.”

National Association of Primary Care chair Charles Alessi said the principles were a “useful starting point as long as they are not interpreted inflexibly”.

“I can see if people go in with hobnailed boots and say ‘this is right’ and ‘this is wrong’ without understanding the natural communities that exist, it isn’t going to work,” he added.