Figures obtained byHSJ this week reveal huge variations in the amount GP practices are paid for doing their job, regardless of how many patients they serve or the severity of their needs.

The reason? The minimum practice income guarantee. This guarantee, introduced in 2004 with the national GP contract, means that the “global sum” formula - used to ensure payments reflect need and numbers - makes up only one part of the total. The rest is a supplement agreed to ease GPs into the new contract.

The outcome is that while, on average, the supplement accounts for around 20 per cent of the total payment, in some cases it is more like 50, 60 or 70 per cent. In HSJ’s survey of 16 primary care trusts, there were two GP practices where the top-up alone was more than the amount paid through the formula - meaning the GPs are paid almost twice as much as the average for each of their patients.

Our research reveals for the first time the full extent of just how much the income guarantee leads to variations that undermine any notion of equity. As PCTs point out, this means payments bear no relation to the quality of services provided. This is not just unfair, it works against the government’s aim of reducing health inequalities. It also means that even if patients desert a practice in droves, the GP does not feel it where it hurts.

There is disagreement between doctors and employers over how long the income guarantee was intended to remain in place. Either way, four years is a long time for a transitional payment costing upwards of£300m a year. With no announcement expected before Lord Darzi’s report in the summer, the 2008-09 GP contract will have to include it too.

The government must announce the phase-out of the guarantee with a clear timetable. The costs of the supplement could be put to far better use.