Four Muslim Labour MPs have been sent suspicious packages over the last 48 hours with copies of a 'Punish a Muslim' letter that calls for violence against Muslims.

Rupa Huq, the MP for Ealing Central and Acton, was the latest to receive the letter today, after copies were reportedly opened by staff for Rushanara Ali (Bethnal Green and Bow) and Mohammad Yasin (Bedford). A fourth package was sent to the Manchester Gorton MP, Afzal Khan, but was not opened, according to the Guardian.

A member of Huq's staff was today taken to hospital as a precaution after opening the letter, which Huq told the Guardian contained a 'sticky substance' that the police had described as 'low-level noxious'.

This came after two people were taken to hospital yesterday, also as a precaution when a package leaking a suspicious liquid was sent to Yasin's office.

Police are now investigating the 'Punish a Muslim' letter, which has been distributed across the country and details a list of violent acts to be performed against Muslims.

A group which monitors anti-Muslim hate crimes, Tell Mama UK, said that it had received reports of people in Bradford, Leicester, London, Cardiff and Sheffield receiving the letters.

Huq told the Guardian that she had been assured that the substance was not harmful. But, she said: 'It is horrible though, it's really very frightening. It is to put the frighteners on us but we won't be cowed. I'm sure I won't be the last and I'm sure this is part of a pattern of targeting Muslim MPs. Among my colleagues, people have shown support but they are outraged.'

All four of the packages sent to MPs have been found in the Norman Shaw north building in the parliamentary estate, which is linked by a walkway to Portcullis House.

A parliamentary spokesman confirmed that four packages had been sent to the building in recent days and that police were investigating the latest package.

The spokesman added: 'This is further to the two items investigated yesterday, both of which were found to be non-harmful. The police are investigating the content of the letters to identify any potential link.'

A Metropolitan police spokesman said: 'Police were called at 9.49am on Tuesday, March 13 to reports of a suspicious package at Norman Shaw Buildings, Victoria Embankment, Westminster. Specialist officers have been called and the package will be assessed.'