A cross-party committee has claimed Welsh schools are operating under an outdated "funding fog".

The Welsh assembly's school funding committee said in a new report released on Wednesday that the distribution of budgets is based on confusing criteria and old data.

The report drew back from suggesting that pupils suffer from a "postcode lottery" in education but said there are "real differences between school funding in different parts of Wales".

It found that the formula for allocating cash uses figures from previous years' intakes of pupils rather than predictions of future needs.

It also suggested that the assembly government's preferred means of measuring poverty - by the number of pupils receiving free school meals - may not be the most appropriate.

And it disclosed that not all local education authorities distribute money in the same way, leading to further inequalities.

The assembly members called for an immediate review of council formulas "so that the education element is based on the current and future costs of providing education services rather than on historic costs".

Committee chairman and Conservative education spokesman William Graham said the group was left with the perception of "a complicated and unresponsive system where accountability was scattered and unclear".

Welsh education minister Jane Davidson declined to respond to the series of recommendations made in the report.

But Plaid Cymru education spokesman Janet Ryder said ministers should adopt some of the calls made within it, including three-year funding cycles for schools

"This report raises grave concerns about the way our schools are being funded and current funding levels," she said.

"Schools need stability and funding arrangements to allow them to plan for the long term - a three-year funding cycle would help achieve this."

And Welsh Liberal Democrat education spokesman Peter Black agreed.

"This report will put Liberal Democrat principals at the heart of education policy in Wales," he said.

"We have been promoting the idea of three-year budgets for a very long time so as to bring stability to school finances, but despite promises, the government has failed to deliver.

"This report will add to the pressure on the education minister to ensure her good intentions are put into action."