Pupils will be offered an extra 100m hours of tuition under post-pandemic catch-up plans unveiled today – but the government faced immediate criticism of the £1.4bn programme, with its own tsar warning “more will be needed”.

After months of unprecedented school closures, £1.4bn will be spent on up to 6m sets of 15-hour tutoring courses for disadvantaged pupils as well as an expansion of an existing fund for helping 16- to 19-year-olds with subjects such as English and maths, the Department for Education (DfE) said.

There is also provision for extra training and support for teachers, and funding to allow some year-13 students to repeat their final year if it was badly affected by the pandemic.

It gave no immediate verdict on mooted plans to extend schools days by 30 minutes. This idea, criticised as misplaced by some teaching unions, will be the subject of a separate review due to report later in the year.

On the new spending plans there was virtual unanimity from unions that the sums committed were insufficient, with the National Education Union calling them “inadequate and incomplete”.

Perhaps even more damaging for ministers, the announced spend is about a tenth of the £15bn total understood to have been recommended by Sir Kevan Collins, who was appointed in February by Downing Street as the education recovery commissioner tasked with leading efforts to make up for the damage done by the coronavirus pandemic, particularly to pupils from more deprived backgrounds.

The official announcement of the new plan carried laudatory quotes from Gavin Williamson, the education secretary, and Boris Johnson, the prime minister, who said it “should give parents confidence” – but the quote released from Collins was more circumspect.

Ensuring all pupils would catch up “will require a sustained and comprehensive programme of support”, Collins said, and while the latest announcement would help many children and teachers, “more will be needed to meet the scale of the challenge”.

Government sources stress that the total announced for all catch-up work over the past 12 months is now closer to £3bn and that ministers have pledged to implement a long-term plan for the process.

Mary Bousted, the joint general secretary of the National Education Union, said: “Rarely has so much been promised and so little delivered.” The amount promised showed that the government “does not understand, nor does it appreciate, the essential foundation laid by education for the nation’s economic recovery”, she added.

The National Association of Head Teachers (NAHT) called the investment “paltry” when compared with plans in other countries and with the amount spent on supporting businesses.

“After weeks of talking big and building expectation for education recovery, this announcement only confirms the government’s lack of ambition for education. It’s a damp squib,” said Paul Whiteman, the NAHT’s general secretary. “Education recovery cannot be done on the cheap.”

The Association of School and College Leaders condemned what it called “a hugely disappointing announcement which lets down the nation’s children and schools at a time when the government needed to step up and demonstrate its commitment to education”.Ideas for extending the school day could prove controversial if implemented, as reportedly recommended in Collins’s report to ministers. Polling has shown it is not hugely popular with parents, while unions have warned about the impact on family time and out-of-school activities.

Of the government’s tutoring plans, an extra £218m will go towards the national tutoring programme, which provides external support, with £222m for tutoring for those aged 16 to 19.

The biggest chunk, £579m, will be for “local tutoring” – in-school services using new or existing staff. This will cover about 75% of the total costs, with schools contributing the rest. In the coming academic years, the proportion paid by schools will rise so that they eventually meet most of the tutoring costs, the DfE statement said.

Labour at the same time unveiled its party plan for educational recovery, pledging an extra £14.7bn over the next two years to ensure pupils catch up and to reduce extra attainment gaps created by the disruption.

Particularly focused on the wellbeing of students following the pandemic, the money would be spent on areas including additional breakfast clubs and activities for children, giving them more time to socialise and better mental health support.

The Labour plan would commit to small-group tutoring for any child requiring it, more support for teachers, an “education recovery premium” to guarantee more spending on children who have faced the greatest disruption, and free school meals extended across all holidays.

The shadow education secretary, Kate Green, contrasted what she called Labour’s “bold plan” with the commitments made by the government.

Speaking of the government’s plan, Green said: “This announcement makes a mockery of the prime minister’s claim that education is a priority. His own education recovery commissioner has all but said this plan is insufficient. Sir Kevan Collins told ministers that 10 times this level of investment was needed to help children recover.”

In a statement released with the plans, Johnson said: “Young people have sacrificed so much over the last year and as we build back from the pandemic, we must make sure that no child is left behind.

“This next step in our long-term catch-up plan should give parents confidence that we will do everything we can to support children who have fallen behind and that every child will have the skills and knowledge they need to fulfil their potential.”