Analysis of the three main parties' childcare pledges by childcare business advisers Christie & Co concluded that a pledge in the Conservative manifesto to "assess what more is needed" to provide high-quality childcare based on examples from Europe and across the world indicates childcare ratios are set to be reviewed should they be re-elected.
While in coalition government the Conservatives looked at lowering staff-to-child ratios, in a report childcare minister Liz Truss's More Great Childcare report. However, the plans were scrapped following criticism from the childcare sector.
Claims the idea could be revisited come just months before the free childcare entitlement is doubled from 15 to 30 hours a week for all three- and four-year-olds.
"Part of the Conservative manifesto touched upon looking to Europe and further afield for best examples of childcare provision," Courteney Donaldson, Christie & Co's head of childcare and education, said.
"We feel that this is a prelude to the opening of discussions around childcare ratios, a discussion previously dismissed by the party back in 2014 following Liz Truss's widely condemned report."
Concerns are also raised by Christie & Co over Conservative plans to increase capital investment to build nurseries next to primary schools.
"Whilst more nursery settings close to primary schools could be welcomed, these settings are often only open during term time and from 9am to 3pm - hardly suitable for working families," added Donaldson.
Christie & Co also calls into question a pledge in the Labour Party manifesto for a transition to a graduate-led workforce.
"We are well aware that staff wages and the retention of staff is a huge challenge for the sector and the introduction of a graduate-led workforce would only exacerbate these issues," said Donaldson.
Meanwhile, a Labour pledge to roll out education provision from the end of maternity leave would need to be backed by significant extra funding, the firm said.
The Liberal Democrats' manifesto also focuses on a graduate-led workforce, with each setting employing at least one graduate. In addition, the Liberal Democrats also propose to increase the early years pupil premium to £1,000 per pupil per year.
Donaldson said all three manifestos "are ticking boxes to appease the masses but without being able to guarantee extensive funding for the sector".
Purnima Tanuku, chief executive of the National Day Nurseries Association, said: "Instead of revisiting ratios or promising capital investment for nursery schools, the next government needs to look at the way the funding is allocated and invest adequately in its ‘free' childcare policy.
"The previous government promised an average hourly figure of £4.88 per child in England which has since dropped to well below £4. This is just not sustainable for private and independent nurseries which deliver the lion's share of ‘free' childcare hours.
"Nurseries are the experts in this area and know their own children's needs. They should be left to deploy their staff within the current legal requirements in the best way in order to continue to deliver the high-quality early years education which gives all our children the best start in life."
Neil Leitch, chief executive of the Pre-School Learning Alliance, said: "It was not so long ago that the Department for Education was using early years practice in other European countries to justify the attempt to relax ratios - and yet, as we've learned from the failure of both that policy and childminder agencies, trying to replicate policies from other countries simply doesn't work.
"We're clear that we will oppose any attempt to reopen the ratios debate, or introduce any equally misguided early years policies, by any political parties - and we've no doubt that any such moves would be roundly rejected by both the sector and parents as well."
The Conservative Party has been contacted for comment.