Another suspected gas leak at the Feltham Health Centre sparked an evacuation on Tuesday morning.
The cause behind the possible leak - the second alarm in just over a week after dozens of vistors were ushered out of the Feltham High Road centre on Monday following a false alarm - is yet to be confirmed.
Following last week's scare (pictured) centre bosses claimed there was no fault but their handling of the incident was criticised by patients who said they were kept in the dark as events unfolded.
Ann Woolnough, spokeswoman for Hounslow Primary Care Trust, confirmed its staff were investigating unconfirmed reports of a gas leak.
"People think they are smelling gas and as a precaution the health centre has been evacuated," she added.