Violence has flared up at an asylum centre where detainees sleep on tent floors in filthy conditions without bedding, it has been claimed.

“At least one incident of sexual violence” has occurred at Manston processing centre in Thanet, with asylum seekers going hungry in disease spreading conditions, the Public and Commercial Services (PCS) union has said.

It comes after Downing Street said this week it moved more than 1,000 migrants from the facility near Ramsgate, amid reports of a diphtheria outbreak.

Union spokesman Paul O’Connor, said: “We’re aware of detainees sleeping in cold, overcrowded marquees on the floor without bedding; of incidents of violence including at least one incident of sexual violence; of self-harm and suicide attempts; of filthy toilets; of appalling sanitation; of infectious disease spreading due to conditions; and of people going hungry.

“The home secretary is acting outside the law, as her own minister acknowledges, and there are, we believe, many detainees now held illegally at Manston,” he told The Guardian today.

Mr O’Connor’s remarks came as the union joined a legal action against the home secretary over poor conditions at the centre for processing small boat arrivals.

It follows damning reports asylum seekers were abandoned at London’s Victoria Station on Tuesday night.

Eleven men were bussed to the capital as part of a larger group and left confused and scantily clad, with one spending the night sleeping rough on city streets.

Speaking in the Commons yesterday, MP Alistair Carmichael called for Suella Braverman to answer for the incident.

On Friday the home secretary took a trip on-board a Chinook helicopter as she travelled 19 miles between Dover and Manston.

The high-grade military helicopter, which can reach speeds of 187mph, was spotted in the skies above east Kent.

No.10 has since defended its decision to use the helicopter - which experts for the UK Defence Journal say costs about £3,500 per hour to fly.

A spokeswoman said: “The home secretary was in Dover to receive an update on operations on the ground.

“That obviously involved operations in the Channel.

“She travelled on a military aircraft to see the area of operations at sea.”

The PCS is the UK’s largest union for civil servants. Its members include Border Force staff and enforcement officers.

The Home Office has been approached for comment.