On 23 March, the prime minister announced a nationwide lockdown to slow the spread of coronavirus. “I must give the British people a very simple instruction – you must stay at home,” said Boris Johnson. Dominic Cummings certainly ignored that diktat, along with government guidance not to travel anywhere else to self-isolate. But did he break the law? On 26 March, regulations were introduced in England that made it an offence to leave home without a “reasonable excuse” and to gather in groups of more than two. The Health Protection (Coronavirus, Restrictions) (England) Regulations 2020 gave police powers to forcibly return those who refused to comply with the lockdown to their homes and issue fines to dissenters. We know Cummings went to Durham after the regulations came into force. He was seen running away from Downing Street on 27 March and was definitely in Durham by 31 March, when officers from the local police force spoke to his father. Downing Street has not contradicted a witness who told the Guardian they also saw Cummings in Barnard Castle, 30 miles from Durham, on 12 April. Whether he contravened the regulations depends on the definition of “reasonable excuse”. The regulations do not define the term but they do provide non-exhaustive lists of reasonable excuses to be outside, such as shopping for necessities, doing exercise and travelling to and from work. Even when Boris Johnson announced a slight relaxation of lockdown in England on 11 May – when he said “you can drive as far as you like to reach an outdoor space” – that was specifically only for the purpose of exercise. Asked by reporters on Saturday for her reading of “reasonable excuse”, the deputy chief medical officer, Jenny Harries, suggested “extreme risk to life” would fit the bill. “If you’re symptomatic, you stay at home, take yourself out of society as quickly as you can and stay there, unless there’s extreme risk to life,” she said at the daily press conference. Downing Street’s statement says Cummings travelled 260 miles north “owing to his wife being infected with suspected coronavirus and the high likelihood that he would himself become unwell. It was essential … to ensure his young child could be properly cared for.” The regulations are clear that had Cummings been stopped by police en route to Durham, officers could have directed him to return to London and fined him. The wording of the regulations says police only need to “consider” (ie believe) that someone had left home without a reasonable excuse in order to send them back. The government had already issued non-legally-binding guidance that said people should not leave home to isolate elsewhere: “Essential travel does not include visits to second homes, campsites, caravan parks or similar, whether for isolation purposes or holidays. People must remain in their primary residence. Not taking these steps puts additional pressure on communities and services that are already at risk.” Theoretically, police could also have sent Cummings back to London using another new law, the Coronavirus Act 2020, which gave police further powers to remove a potentially infectious person for screening/assessment and also to detain them if they refuse to comply. But whether the police can retrospectively fine someone considered to have broken the rules is unclear.