Every week I do an advice session for people in my capacity as member of parliament. People who live in my district come to see me with their many problems. And every week, without fail, I will see one or two Jamaicans who have entered Britain illegally, but are somehow managing to survive. Quite often they look and sound like they have never left Jamaica.

It is always baffling to me that perfectly respectable Jamaican professionals can have such difficulty obtaining their visa and entering the UK while persons who are less than respectable appear to slip in and out of the country relatively easily. Many Jamaicans in the UK illegally came for a short visit and just stayed.

Over the years it has become increasingly difficult for persons who have entered the UK illegally to survive. Most employers now insist on checking your papers. But there are still some jobs to be obtained where you will get paid cash in hand. And sometimes people settle in the UK, having entered illegally, and live for years undetected.

Problems often arise for the first time when a relative is sick and they need to return home. I have to explain to them that they can leave if they wish, but they will never be able to re-enter the country because their papers were not in order in the first place. Sometimes it is only when their children grow up and want to go to college that their parents have to admit to their offspring that, because they themselves are here illegally, their children will not be eligible for normal student support.

I often have to explain that, if they had tried to regularise the situation earlier, something perhaps could have been done. But they have now left it too late. Twenty years ago, when I first became an MP, it was quite common for me to appeal to the authorities on humanitarian grounds and get illegal “overstayers” regularised. Nowadays the authorities show no mercy.

Recently the British authorities set up Operation Nexus. This is about enhanced co-operation between the police and the immigration authorities. Typically, immigration officers are posted in police stations. There they move in swiftly to deport anyone who has been arrested for a crime and who has any question mark over their immigration status.

The operation is worth running because so many London criminals are from overseas. Currently 27 per cent of the people arrested for a crime in London are foreign nationals, 25 per cent are gang members and 15 per cent sex offenders. The Metropolitan police are aiming to pass 100 files every week to the UK Border Agency in order to remove 2,400 suspected criminals from the UK this year.

A typical case is Jamaican Lincoln Farquharson. He was charged with a string of sexual offences, but was never convicted. But he was deported last month after police passed files to the immigration courts. The files revealed that he had been arrested five times between March 2006 and April 2011 for multiple rapes and violent assaults. The Metropolitan police hailed his deportation as “the removal of a dangerous man from our shores”.

So Jamaicans who are thinking of entering the UK on a six-month visitor’s visa and just staying should think twice. Year by year the system gets tougher and more merciless.

Diane Abbott is a British Labour Party MP and spokeswoman on public health

www.dianeabbott.org.uk