Britain put the controversial measures in place in the middle of last week, and for the first time ever British immigration officers are working on foreign soil, screening potential visitors before they've left their home country. Zbynek Havranek is the spokesman for the British Embassy; earlier this week I asked him what passengers could expect when they stepped behind the screen for a chat.
"It's exactly what happens and what has always happened on arrival in the U.K., with the exception that now this process is carried out at Prague Airport as well. So basically people are asked questions that should confirm their reason for travelling to the U.K., and questions that will establish that they're really travelling for the purposes that they state they do - i.e., if they claim they're travelling as tourists, they need to make it clear to the consular officials that that's really the case and that they are coming back."
Britain says the "pre-clearance controls" - to use the official jargon - have been put in place to prevent the "continued, systematic abuse of [the British] immigration and asylum system by some Czech citizens." You won't find a British official to admit it publicly, but those Czech citizens are almost exclusively members of the Roma minority, who say they are subject to widespread racial discrimination at home. But the new immigration controls have themselves led to allegations of racism: allegations that Britain categorically denies:
"We are doing the pre-clearance control on the basis of immigration rules, not ethnicity or nationality. As far as we can tell, the refusals include people of various nationalities or ethnic groups."
So you can confirm that it's not just Roma who are being turned away.
"Yes, I certainly can. But as I say, we really don't make any difference. We don't monitor who is Roma, who is a Czech national, who is a foreign national. What we know is people who were refused."
Mr Havranek was speaking to me before this week's sting operation by Czech Television. On Monday Czech TV sent two reporters - one Roma, one 'white' - to London, with identical tickets, purpose of visit, hotel accommodation and amounts of money. The 'white' reporter was allowed through, the Roma reporter was turned away. The British Embassy remains unrepentant: the measures are not discriminatory, says British charge d'affaires Denis Keefe. The Czech government agrees: Foreign Minister Jan Kavan says the reporter was lying.
But many people are now beginning to point out that whether the "pre-clearance controls" are discriminatory or not is becoming increasingly irrelevant. As long as the measures look like discrimination, then Britain has a major public relations disaster on its hands.
And some critics say Britain - scene of a fierce debate over "bogus asylum-seekers" and "economic migrants" in recent years - is simply wasting its time. Klara Vesela-Samkova is a lawyer who works with the Roma community:
"I can say only one thing. If the British government really suppose that they will help themselves, they are really foolish. Because for Roma, borders were never a problem, even in the time of Communism. And if it is not possible now to go through Prague's airport, they will find another way. And in any case, they will go where they want. So it's foolishness."
And tune into next week's edition of Talking Point, when Rob Cameron will be looking more deeply into this highly controversial issue.
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