Serious questions have been raised over Britain's border security after a BBC journalist entered the UK twice on fake and stolen passports.
Shahida Tulaganova obtained 20 illegal passports - each from an EU country, including the UK - within months.
Those in the trade told her to travel via sea or bus, saying port security was less stringent than airports.
The Home Office said it works closely with the EU to tackle the crime, taking the issue of false documents seriously.
In 2004, 8,285 fraudulent documents were detected at UK ports of entry, according to Home Office figures.
Entering the UK on a fake or stolen passport carries a maximum sentence of 10 years in jail, while making a false statement to obtain a passport can lead to a prison sentence of up to two years.
Shahida travelled across Europe to obtain her false documents for her Panorama investigation.
They ranged in price from just £250 to more than £1,500. Some were provided within several days, while others took weeks.
She found her first illegal passport dealer in the centre of London - through an advertisement in a Russian language newspaper.
The dealer - Henry - provided her with a genuine Czech passport, by getting someone who looked like her to apply for one, using her photo.
Shahida's investigation poses questions over the number of non-EU nationals entering Britain on illegal passports. She uses Poland as an example.
"Since [Poland] country joined the EU less than two years ago a quarter of a million Poles have left and legally registered for work in Britain," she says.
"But if my contacts are right, many of these may not have been Poles at all, but illegal immigrants using fake passports."
Czech Republic, Poland
Shahida enters Britain via boat - from Spain to Portsmouth - on a fake Latvian passport, and then later on the Eurostar using a stolen Estonian passport.
Despite information on stolen passports being registered to a central Interpol database, her Estonian passport goes undetected.
The Home Office says there is a "comprehensive bilateral exchange of information between member states regarding the issue of lost and stolen EU passports".
It maintains that in addition to this, all immigration officers are highly trained in identifying false documents.
"All our immigration officers at British ports are trained in forgery detection techniques and have access to specialist forgery detection equipment," a spokesperson said.
The government has also introduced biometric e-passports with images securely stored inside chips, in an attempt to combat forgery and improve the security of British passports.
Panorama: My Fake Passports and Me was on BBC One on December 4 2006.