The Ham&High and our readers were equally confused by smoke and noise coming from the Royal Free Hospital last Thursday and Saturday night

Eagle-eyed Hampstead observers have been writing in to the Ham&High about smoke and noise coming from the Royal Free Hospital in Hampstead last Thursday and Saturday.

Belsize Park resident Ron Vester said: “Sometimes all day one hears a loud burst of noise from roof of hospital.

“One can hear it from The Boating Pond in Highgate.

“Does anyone know what this is, are they burning remains from surgery as some suggest or syringes?”

“I do know this is close to my flat in Belsize park and wonder if this is dangerous to those who live downwind.”

We have since learned that the Royal Free uses steam circuits to heat the hospital and one of the valves blew away on Thursday.

The valve was repaired, but it blew away again on Saturday night.

Our readers will be interested to know the valve has since been replaced.