Under the proposals, councils are preparing to provide 1,140 funded hours for all three and four-year-olds - and eligible two year-olds - to improve outcomes for children and to support parents to work, study or train.

A report prepared for the auditor general and Accounts Commission says providing those hours will require a large increase in the number of childcare staff and changes to premises, which will be difficult to achieve in the time available. Detailed planning by the government should have been started earlier to help councils meet the 2020 deadline.

In addition, councils estimate they will need around £1bn of annual revenue spending on funded early learning and childcare by 2021/22 but the Scottish government's indicative figure for annual revenue funding is around £840m.

They also believe that creating the infrastructure will cost £290m more than the Scottish government’s £400m prediction, and will require 12,000 whole-time equivalent staff compared to government estimates of between 6,000 to 8,000.

The report also assessed the government’s earlier 2014 expansion of funded early learning and childcare to 600 hours. The findings show the government did not identify measures of success before committing almost £650m to the increase, making it difficult to assess whether it is delivering value for money, and the expansion was agreed without evidence that it would achieve the desired outcomes for children and parents and without considering other ways of achieving those objectives.

While parents were very positive about the benefits of funded hours to their children, Audit Commission research found parents said funded hours had a limited impact on improving their ability to work.

Caroline Gardner, auditor general for Scotland said: ‘Focussing on the early years has the potential to make a real difference to young peoples' lives but the Scottish government was not clear enough about what the expansion of funded hours in 2014 was expected to achieve.

‘We are encouraged that the Scottish government is now planning better for how it will assess the impact of the expansion to 1,140 hours and has already published some baseline information.’

Graham Sharp, chair of the Accounts Commission, said: ‘The scale of change needed over the next two years is considerable and there are significant risks that councils will be unable to deliver that change in the time available.

‘There is now an urgent need for plans addressing increases in the childcare workforce and changes to premises to be finalised and put in place.’

Accounts Commission report Early Learning and Childcare is here.

Report by Pat Sweet