A package believed to contain white powder was sent to MPs offices at the Houses of Parliament today.
Wristbands, one of which read multiculturalism is genocide, were also in the suspicious package, reports claim.
Eight police officers gathered in One Parliament Street on the fourth floor.
Its believed the package was sent to the shared office of Labour MPs Jo Platt and Anna McMorrin, but was addressed to MP Platt, who has represented Leigh, Greater Manchester, since 2017, Mirror Online reports.
Three people complained of itchy eyes, police said.
A spokesman for the House of Commons told the paper: Today a suspicious item of mail in an office in the Parliamentary Estate was investigated by the Met Police and was found not to be harmful.
The immediate area was closed as a precaution but access to the building was otherwise unaffected.
The London Ambulance Service attended as a precaution.
A Met Police spokesman told Metro.co.uk: Police were alerted at 4.20pm on Wednesday October 10 to a report that three people were suffering ill-effects, such as itchy eyes, having opened a package that had been delivered to an address in Parliament Street.
The package and its contents have been assessed and are not thought to be harmful.
LAS attended the location as a precaution. The three people did not require medical treatment.
A London Ambulance Service spokesperson said: We were called at 4:34pm today to Parliament Street, Westminster to reports of an incident.
We sent an incident response officer and an ambulance crew to the scene. We also dispatched our hazardous area response team (HART).
We assessed three people at the scene, but did not take anyone to hospital and our crews were stood down.