Reform UK and the Green Party are investigating over Islamophobic and antisemitic comments made online.
Hillingdon is the home of Heathrow Airport, and the local council is up for election on 7 May.
The garden centre in Hillingdon was run by volunteers with learning disabilities.
Hillingdon Council is considering a legal challenge to prevent housing asylum seekers in its hotels.
Hillingdon Council says it is spending thousands supporting Chagossians arriving in London.
More than 4,500 have signed a petition urging Hillingdon Council to keep the Colham facility open.
The council currently houses about 3,000 asylum seekers placed in the borough by the Home Office.
Hillingdon Council wrongly cut care support for a vulnerable man for three months.
