They were leading a Q&A session while sitting in front of a sign setting out infection control instructions, including the requirement to wear a face covering in the hospital. Mrs Tedford was also pictured without a mask at another session on June 30.
It later emerged that the source of the outbreak was thought to have been a training event also held on June 30.
A nurse who had unknowingly contracted the virus was believed to have attended the presentation and unwittingly infected 16 others.
A number of staff reportedly failed to wear masks or distance themselves from others – particularly during the lunch break.
The CQC is understood to have made an unannounced visit to the hospital on August 4, following reports of the outbreak.
The regulator issued the section 31 notice on August 7, details of which are expected to be published this week.
A week later, on August 14, Sir Amyas Morse, who chairs the Hillingdon Hospitals NHS Foundation Trust, said he had accepted Mrs Tedford’s resignation with immediate effect.
“Sarah has reached a personal decision to stand down for family reasons, a decision I respect and understand,” he said at the time.
Mrs Tedford added: “I joined the NHS as a student nurse in 1985, and I have always strived to do my very best for my patients and colleagues. However, recent months have really caused me to reflect about working so far away from my family.”
Last week Sir Amyas told the trust’s board that the CQC had “pointed to areas where we could and should improve our infection control practices.”
Mr Acheson said: “We have taken urgent enforcement action against the trust to ensure that safety risks are addressed. We will provide further information when the legal process allows.”
A spokesman for Hillingdon Hospitals NHS Foundation Trust said: “We have taken immediate action to improve safety and believe that we are making progress. We want to assure our staff, patients and the wider community of our absolute commitment to their safety and wellbeing.”
Mrs Tedford could not be reached for comment on the CQC intervention.