I just looked to confirm the figure 516 and right enough if you go here
https://coronavirus.data.gov.uk/healthcare right enough you will see
Patients on ventilation : 516
but if you drill into the link you will see it says
"England figures are the numbers of COVID-19 patients in beds which are capable of delivering mechanical ventilation and includes Nightingale hospitals. Data are reported daily by trusts to NHS England and NHS Improvement. "
All you can determine from this is there are 516 patients that have tested positive for COVID are in a bed that is capable of mechanical ventilation.
I don't know if its set out like this to deliberately mislead but that's what happens as the statement "516 people being ventilated" gets repeated when its not factual.