JUST when Tony Blair and his New Labour government do something to make you think politicians couldn't possibly sink any lower, the Tories remind you that they still have no rivals when it comes to sheer nastiness.

Tony and his cronies have hardly been distinguishing themselves lately. Whatever the circumstances surrounding the dismissive suggestion by a senior Downing Street official that Government scientist Dr David Kelly was a "Walter Mitty" figure, it leaves a nasty stink - particularly because it came a couple of days before Dr Kelly's funeral today. In the wake of the orgy of finger-pointing and recrimination that followed Dr Kelly's death, no wonder Labour poll ratings are plummeting.

Then the Tories remind everybody why we all voted them out of power so comprehensively six years ago.

Their latest wheeze - sorry, well-thought-out, considered proposal - is to subject every would-be immigrant to this country to screening for infectious diseases before allowing them in.

No doubt the Tories - who have twigged to the fact that many people are worried about immigration - think this will appeal to the worst instincts in all of us: instincts to which they have successfully appealed in the past.

What shadow health secretary Liam Fox appears to want are new powers to ensure any 'migrants' who are at risk of spreading infection - or of becoming a long-term financial burden to the NHS - can be screened out before they arrive and excluded from Britain.

What's wrong with that, you may say? Only sensible.

I'll tell you what's wrong.

Firstly: the hidden text - the association that will be made in many people's minds - is that immigrants are dirty and diseased. The proposals are bound to stir up prejudice at a time when racial tensions in this country are already high - and the Tories must know that.

Secondly: some experts says compulsory screening of immigrants would drive many who are HIV positive underground - encouraging them to enter the country illegally, thus adding to the problem of illegal immigration and making it impossible to keep track of the spread of HIV and other conditions.

Thirdly: it may be tempting in these days of ever-greater demand on our health service to try to keep it for ourselves.

But anyone accepted for immigration to this country - on whatever grounds - should be entitled to access the health care this nation prides itself on.

Underlying the Tories' agenda is the hidden assumption that immigration is bad: that immigrants are a bunch of scroungers who want to live off the fat of the land we have created.

Nothing could be further from the truth. Many immigrants are hard-working, determined, ambitious people who bring fresh blood and new ideas to a country that desperately needs them.

Throughout its 2,000-year history Britain has thrived thanks to successive waves of immigrants - Romans, Saxons, Danes, French - who have together enriched our collective culture and made us who we are. The same is true of immigration today.

Subjecting anyone who wants to live in this country to compulsory screening is demeaning and insulting to them as human beings and may stop them wanting to come altogether.

Exactly the point, the Tories may say. But if we pull up the drawbridge and refuse to let anyone in, we as a nation will be greatly the poorer for it.

And we would soon realise it.

Updated: 11:18 Wednesday, August 06, 2003