THE United Kingdom Border Agency has admitted it "made no effort" to track down 120,000 missing asylum seekers and immigrants, it has been claimed.
Many of those will have entered the country through the Port of Dover and the Channel Tunnel.
A local MP said that the revelations come as "little surprise" and stem from a legacy left by the last Labour government.
The Home Office has admitted regular security checks were not carried out despite UKBA assurances they were, said independent chief inspector or borders and report author John Vine.
Cases were effectively archived in order to meet a summer 2011 deadline.
MP Charlie Elphicke said: "I'm not surprised by this.
"It merely cements my long-held belief that we must have robust borders and adequate staff to operate the front line."
The UKBA conceded that its failures have led to asylum seekers and migrants –- who would otherwise have faced removal from Britain via centres like the Immigration Removals Centre in Dover – gaining rights to remain in the UK.
More than 37,000 were effectively written off as there was no apparent trace of them.
The report also outlined that UKBA staff was so overwhelmed with work that at one point more than 150 boxes of post, including letters from applicants, MPs and their legal representatives, simply lay unopened in a room in Liverpool.
As long ago as 2006, the then New Labour Home Secretary John Reid pledged to deal with the backlog within five years. It was a promise met with scepticism at the time.
The following year, it was disclosed that 450,000 cases lay in a backlog.
Tens of thousands of those cases would have had their roots in the asylum crisis after 1997 when people claiming asylum poured into Britain on lorries via ferries and on freight trains through the Channel Tunnel.
The flow of migrants and their families was halted in late 2002 when the Red Cross refugee centre – the so-called departure lounge to Britain – was shut down and demolished.
Calais has, however, remained a centre for people-traffickers to ply their trade.
A parliamentary committee found earlier this month that it was still struggling to deal with more than 300,000 unresolved cases, a figure equivalent to the population of Iceland.
Sir Andrew Green, chairman of the Migration Watch UK campaign group, added it was "another chapter in a sorry tale" and the fundamental problem was the UKBA is "seriously under-resourced. . . reduced to sticking fingers in the dyke".
In his report, Mr Vine said: "On the evidence I found, it is hard not to reach the conclusion that cases were placed in the archive after only very minimal work in order to fulfil the pledge to conclude this work by the summer of 2011."
Asylum cases placed in the archive did not receive the regular six-month checks against either the Police National Computer or the Home Office warnings index watch-list which the agency had promised to carry out, the inspectors found.