Officers forced their way into the house on Staines Road, Bedfont a short time later and found the bodies of four people inside.
Police said they believe they know the identity of the four people, thought to be a man and woman in their 30s, an 11-year-old girl and a three year-old boy. All four are thought to be related.
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However, enquiries are underway to formally identify the four people and inform their next of kin. The Met’s investigation is led by homicide detectives from Specialist Crime.
Chief Superintendent Sean Wilson, local policing commander in west London, said: “Our investigation is at a very early stage, and based on our initial enquiries, we are not currently seeking anybody else in connection with the incident.
“I know the shock and distress that this terrible incident will cause among the community in Hounslow and beyond. I can assure local people that specialist officers are working to establish exactly what happened and I will provide further information as soon as I can.
“I am also aware that this incident will be particularly upsetting for children, and I ask people to please be responsible about what they post on social media, including not naming or speculating as to the names of those who’ve died.
“There will be additional police officers in the area across the weekend, I urge anyone with information or concerns to speak with those officers.”
More follows on this breaking news story…