Police are appealing for witnesses and information after a woman and child were assaulted in the Fitzrovia area of Westminster.
Officers were called at approximately 17:20hrs on Saturday, 13 January to New Cavendish Street, W1. London Ambulance Service also attended.
On arrival, officers found two victims - a woman, aged in her 40s, and a nine-year-old girl. Both were suffering the effect of having an irritant sprayed at them.
Both were taken to a central London hospital for treatment and subsequently discharged.
The incident happened when the woman, who was in the company of the girl, opened her door after the intercom was buzzed. A female suspect sprayed a substance before running off.
Officers are particularly keen to trace a man, wearing a distinctive orange jacket, who gave chase to a female suspect in the Langham Street area immediately following the incident. They are also keen to speak to anyone who was in the vicinity of the Yorkshire Grey pub on Langham Street who would have been aware of the altercation.
Anyone with information is asked to contact the Westminster Community Safety Unit on 020 7321 8033 or call Crimestoppers anonymously on 0800 555 111.
Three people have subsequently been arrested as part of this investigation.
A man aged in his 50s [A] and a woman aged in her 70s [B] have been arrested on suspicion of conspiracy to commit GBH. A second woman [C], aged in her 30s, has been arrested on suspicion of GBH with intent.
All three have been bailed - [A] to a date in late January; [B] and [C] to a date in mid-February.