The Education Secretary has warned that parents who do not send their children back to school risk putting a “huge dent in their future life chances”, ahead of pupils returning to classrooms this week.

Gavin Williamson has also said he is not considering resigning despite criticism over the exams fiasco, telling The Sun he will instead continue to “graft away”.

In an open letter to parents, Mr Williamson acknowledged that some may have concerns about their children attending school in England for the first time since March.

But he insisted that schools are safe, detailing measures which have been put in place to minimise infection, while reassuring parents that the health risk posed to children by Covid-19 is “extremely low”.

“If a child is not in school, they stand to lose far more than just a few months of learning. It could well put a huge dent in their future life chances,” he said.

“Education is a birthright, so let’s make sure we get all children back – back to learning, back to playing and back to being kids again.”

He also told The Sun: “For every day they are out of school, we don’t get that day back.

“I’ve seen it with my kids, how much they’ve missed school, missed their friends, missed learning.”

It comes after teaching unions condemned the Government for releasing last-minute guidance for secondary schools in lockdown areas, which includes a “rota system” limiting the number of students in attendance at any one time.

Published by the Department for Education (DfE) on Friday evening, it was released just before the bank holiday weekend and only days away from the start of autumn term.

In his letter to parents on Sunday, Mr Williamson said it was “generally accepted” that children’s health and wellbeing is more at risk if they do not go to school.

He referred to a joint statement by the UK’s chief medical officers, which said “very few, if any” children and teenagers would come to long-term harm from the virus solely by attending school.

Some of the measures highlighted by the Education Secretary include children being put in groups, or “bubbles”, to limit contact, while face coverings should be worn in communal areas of schools under local lockdown.

He said that “huge lengths” have been taken to prepare schools for the return of pupils, adding: “Based on this, our priority now is to get all our children back. It really is the best place for them to be.”

Schools should base their plans on a four-tier system, and the extra measures for secondary schools should kick in at the second tier, according to the latest guidance released on Friday.

All schools remain open at tier one, while tiers three and four mean more stringent restrictions such as closures to all but pupils in vulnerable groups or children of key workers.

A tier two response will see secondary schools and colleges in a restricted area moving to a rota system, which means pupils will spend two weeks on-site followed by two weeks at home.

Labour’s shadow education secretary Kate Green told Sky News that, while the guidelines were “long overdue”, the timing of the release of information was “unfair” to head teachers and school leaders.

Paul Whiteman, general secretary of school leaders’ union NAHT, branded the timing of the new guidance “reprehensible” and said it showed a disregard for the wellbeing of teachers.

“It was obvious weeks ago that lockdown advice was necessary,” he said in a statement.

“The Government’s decision to publish this at 9pm on the Friday of the bank holiday weekend before most schools are due to return is nothing short of reprehensible and demonstrates a complete lack of regard for the wellbeing of school leaders and their teams.”

Mary Bousted, joint general secretary of the National Education Union, said the advice should have been available “months ago”, adding schools had been left to “go it alone” if they needed to organise remote learning.