A man has been arrested by counter terrorism police in Lincoln.
The 35 year old is being questioned as part of an investigation into the so called 'punish a Muslim day' letters - which were posed across the country a few months ago.
He's accused of conspiring to commit murder, as well as sending a hoax noxious substance and malicious communications.
He's now being held at a police station in West Yorkshire.
Searches were carried out yesterday at a house in the south of the city, as well as an office in the city centre.