Eastern European migrants are arriving in London in "unprecedented" numbers, flooding the capital with beggars, pickpockets and prostitutes before the Olympics, officials have warned.
Organised crime gangs are believed to be transporting coach loads of Romanians into the country with instructions to work a pre-allocated "pitch".
Some are understood to have come armed with Google Map print-outs of Marble Arch, which has drawn crowds of rough sleepers in recent weeks.
Authorities are finding up to 60 people with make-shift homes close to the monument and its surrounding streets each night.
Westminster councillor Nickie Aiken, spokeswoman for children, young people and community protection, said: "The reality is that coach transport into London represents an immigration sieve.
"There are no effective border controls on those coming into the UK and making their way to Victoria coach station and we are paying the price of that with a sudden influx of eastern European rough sleepers - especially Romanians - around Marble Arch."
Those being brought into the country are believed to have been lured with the promise of a better future, but they soon end up with no jobs or homes.
"This is being systematically organised from Romania and those running this cynical racket are the only ones who profit from it," Ms Aiken added.
"The problem for London is that one of London's most iconic landmarks is being turned into an impromptu campsite just 95 days ahead of the London Olympics.
"The risk is that we could get a torrent of people coming here from eastern Europe in the deluded belief that London can provide a more lucrative living ahead of the Games."
Officials say they have identified three central London locations which have become "bedding down sites", including Hampden Gurney Primary School in Nutford Place, Westminster.
A second group of Romanians are understood to be commuting into the area to beg or steal.
Checks have shown the majority live in Ilford or Slough and travel by main line trains into Victoria station.
Authorities believe around 50 women were shipped into the Sussex Gardens area last weekend and reports suggest high class prostitutes are working outside the Cumberland Hotel on Great Cumberland Street.
"This influx of same language rough sleepers is utterly unprecedented in scale and nature and we are implementing a strategy to ensure those who do return take a message that rough sleeping in London is not a soft option," Westminster council said.
"This situation is unique as we have never encountered this volume of concentration of such street-based activity and we hope that we are able to deliver a significant reduction in rough sleeping numbers. However we suspect that we may be witnessing the first pro-active, entrepreneurial endeavours by organised criminal enterprise ahead of the Olympics."