Teachers should distance themselves from each other and older students when a full return to school takes place in September, Government guidance says.

The advice says secondary school staff who need to move between classes and year groups should try and keep their distance "as much as they can" - and ideally at two metres from other adults.

Older children should be kept apart from other groups and staff where possible, and they should be encouraged to keep their distance within groups.

The advice comes as the Government has announced that schools will be told to keep children in class or year-group-sized "bubbles".

Whole-school closures may not be necessary if there are a number of confirmed cases of Covid-19 on site, according to Department for Education guidance.

Schools may have "an outbreak" if they have two or more confirmed cases of coronavirus within a fortnight.

The guidance - which looks at how schools will return in September - says the whole site or year group may have to self-isolate at home.

But it adds that whole-school closures "will not generally be necessary" if schools implement the recommended controls.

If there is an outbreak in a school, a mobile unit can be dispatched to test others who have been in contact with the person who has tested positive.

Testing will focus on the person's class, followed by their year group, then the whole school if necessary, the guidance says.

A headteachers' union has warned that it will be "enormously challenging" for schools to keep children apart in year-group-sized "bubbles" in September.

Geoff Barton, general secretary of the Association of School and College Leaders (ASCL), said: "The logistics of keeping apart many different 'bubbles' of children in a full school, including whole-year groups comprising hundreds of pupils, is mind boggling.

"School leaders will have to consider implementing staggered starts, finishes and lunch times, alongside transport to and from school, on an epic scale."

He added: "However, we recognise that the options about how to bring all children back to school in the autumn are limited."

The union is calling on the Government to have in place a "Plan B" in case it becomes clear that a full return to school in September is "just too risky".

On the guidance for a full return to school in September, Paul Whiteman, general secretary of school leaders' union NAHT, said: "Significant time will now need to be spent implementing the new measures Government is asking schools to take."

He added: "The situation seen in Leicester this week has demonstrated that this crisis is far from over, and there will be further disruption ahead.

"It is therefore essential that Government continues to monitor the data when it comes to school return and that it also has a credible Plan B in place should it be required."