It is understood that police are not looking for anyone else in connection with the deaths of three people at a house in north-west London.
Ambulance services confirmed that a woman and two children were found dead at the scene.
A spokeswoman for London Ambulance Service said: "We were called at 6.40pm to reports of an incident in Midcroft, Ruislip. We sent three ambulance crews, two single responders in a car, two officers and our hazardous area response team.
"Sadly three patients, a woman and two children, were dead at the scene."
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A rather cloudy start for most, with rain spreading eastwards, clearing to brighter skies later in the day.
The letter was signed by the CBI, British Chambers of Commerce, the EEF, the Institute of Directors and the Federation of Small Businesses.
A spokesperson said Rory Stewart's remarks were in line with the British government’s stated position.