The chief executive of the hospital that serves Boris Johnson’s constituency, which has shut its A&E unit after an outbreak of coronavirus, has blamed staff for flouting the rules by not wearing masks at work. Hillingdon hospital in north-west London stopped letting patients attend its emergency department or accepting any new emergency admissions on Tuesday after 70 of its staff had to self-isolate. It has had to tell the London ambulance service to take patients from the area to other hospitals because the number of its own staff who are now in quarantine means it has too few personnel to provide a full range of services. The outbreak began last Friday, but its impact on the hospital’s workforce has escalated since then as growing numbers of staff have been identified through the track-and-trace scheme as having been in contact with colleagues who have tested positive and so have had to self-isolate. Hillingdon is the main hospital used by voters in the prime minister’s Uxbridge and South Ruislip constituency, in the London borough of Hillingdon. However, the Guardian can reveal that the hospital’s chief executive, Sarah Tedford, has blamed the outbreak on “irresponsible” staff flouting infection control rules by not wearing a mask while at work, as all NHS staff in England now have to do, and standing or sitting too close to each other. In a message she sent to staff last Friday, Tedford said: “All the way through this [pandemic] we have followed national guidance and it has kept us safe. So what is happening now? I am told some of you are not wearing appropriate masks and you are not adhering to social distancing. This has resulted in an outbreak on a ward where our staff have contracted Covid-19. “If you do not follow the guidance, we cannot keep you safe. I don’t like wearing a mask, but it would be irresponsible of me not to do so. Please think very carefully about what you are doing and ask yourselves if you are keeping yourself safe and if you are keeping each other safe. This is no time to be complacent: we are not out of the woods yet.” She then added: “Can I please remind you to take responsibility for yourself and your team and help us all beat Covid-19? The lockdown is being lifted. Please ensure we play our part in not spreading Covid-19 and leading by example.” Tedford went on: “This is such a serious matter, and at the moment I’m afraid some of us are not demonstrating the behaviour we should be. If you see someone not adhering to the guidance, please remind them of their responsibilities. We all need a little nudge at times.” In a statement on Wednesday, a spokesman for Hillingdon hospitals NHS foundation trust said: “An outbreak of Covid-19 was declared on Friday 3 July 2020. As of Tuesday 7 July, 70 members of staff are now isolating, a number of whom have tested positive for Covid-19. “As a result, the trust has taken the precautionary decision to close Hillingdon hospital to emergency ambulances and emergency admissions. The trust is managing the outbreak in line with Public Health England guidance.” In April the trust was criticised by a healthcare assistant who quit when managers at the hospital refused her permission to wear a surgical mask to protect herself and her patients. Tracy Brennan had self-isolated for 14 days after her daughter had shown symptoms. When she returned to work, she wore a surgical mask she had bought herself, to reduce the risk of her contracting or passing on the infection. But when her bosses told her that the next day she could not do so, she removed it. However, she explained in her resignation letter that managers again told her later that day that she could not wear the mask even though a patient had accidentally coughed into her unprotected face when she was taking blood. In her letter she said: “With a heavy heart and sadness I feel I have no alternative but to hand this letter in as my formal resignation and will be unable to work my notice due to not being allowed to wear sufficient PPE [personal protective equipment] for the duties I perform.” At the time, the trust said it took the safety of all its staff extremely seriously and followed national guidelines. A spokesperson for Hillingdon hospital said: “The vast majority of our staff are maintaining social distancing and it is essential that everyone follows the guidance if we are to provide the safest care to our patients.”