The health secretary, Matt Hancock, has categorically ruled out requiring people to wear face masks in offices, as he hit back at accusations that the new rules stipulating they must be used by shoppers in England were mired in confusion.

People face fines of up to £100 if they do not wear face coverings in shops under rules that come into effect from 24 July, which are designed to reassure visitors to the high street amid the Covid-19 pandemic.

The move, announced by Hancock in the Commons on Tuesday, came after Labour claimed ministers were in a “complete muddle” over the plans, with Michael Gove saying days earlier that face coverings would not be mandatory in shops.

Hancock also sought to play down suggestions that his cabinet colleagues Gove and Liz Truss had sown confusion after they were pictured separately on Tuesday leaving a branch of Pret a Manger, with only the latter wearing a face covering.

On Wednesday, the Telegraph reported face coverings could soon be recommended in all public places including offices and other workplaces, with officials beginning private talks with groups representing major employers.

It came after rules including the requirement that face coverings must be worn in enclosed public spaces such as workplaces were announced in the Blackburn with Darwen area to avoid a Leicester-style lockdown.

However, referencing the Telegraph’s report and asked whether office workers would have to wear masks when they return to work, Hancock told BBC Radio 4’s Today programme on Wednesday: “No, that isn’t going to happen, and the reason is that in offices you tend to spend a lot of time with the same people, and so the way to stop the spread of the virus in offices is to have social distancing, either 2 metres or 1 metre plus mitigations in place.

“The same is true in classrooms, by the way, where if you’re in a classroom, if you’re in a space with the same people repeatedly and for long periods of time, whether an office or a classroom, then a mask doesn’t actually protect them.

“Where the masks benefits is from you spreading the disease to other people when you have relatively short interactions with lots of different people, which is why it’s right to have this as mandatory on public transport, in shops and in the NHS but not in offices where you’re basically there with the same group of people for long periods of time, or in classrooms where the same applies. So it’s following the scientific advice.”

In an interview with Sky News, he added: “We will not be recommending people wear masks in the office.”

Asked about the pictures that emerged on Tuesday showing Gove and Truss apparently conveying a confused message with only the latter wearing a mask leaving a Pret a Manger cafe, Hancock added: “This picture was before we had announced the change in the policy. I announced that change in the policy in the House of Commons yesterday.”

Asked who would be right in wearing a face mask in that store, Hancock said: “Well, the advice until the 24th of July, giving businesses time to make sure that they can get their processes in place and make sure that we can implement this smoothly, the advice now is that face coverings are recommended in shops but not mandatory, that’s been the position for some time and we’re tightening that up to say that they are mandatory from the 24th of July.”

Asked explicitly if from 24 July somebody would have to wear a face mask coming out of Pret, Hancock said: “You do need to wear a face mask in Pret because Pret is a shop … in hospitality, so in a restaurant, there needs to be table service. If there’s table service then it’s not necessary to have a mask but in any shop you do need the mask.

“So if you’re going up to the counter in Pret to buy takeaway, that is a shop, that is Pret operating as a shop. But if you go to your local pub, you can’t go to the pub – in fact there have been stories of people stopping people going to the bar – you can’t go to the bar, and the reason there is the risk of transmission over the bar and therefore it’s table service and a mask is not needed.”

Meanwhile, the prime minister, Boris Johnson, is expected to set out the next steps for the lockdown in a press conference on Friday.