The history of our country and slavery is mixed.

On the one hand, from the sixteenth century, we were one of the great slave nations, exchanging our manufactures for captive Africans and conveying them to slave plantations in the Americas and Caribbean. The ships that brought the slaves returned with the cotton they picked for the weaving mills of industrial Britain.

Our wealth was at the expense of men, women and children who were treated as property – bought and sold at the whim of their masters.

On the other hand, we produced William Wilberforce, MP for Yorkshire, whose Christian faith caused him to question slavery and who eventually persuaded parliament to abolish first the trade in slaves and then slavery itself in 1833. He died three days after the Act was passed.

We thought we would never see slavery in Britain again.

However, the chances are that we have all seen a slave, and some of us have met one. No, we don’t see people with shackles round their necks and the name of their owner branded across their chest.

Modern slavery is hidden.

We now know that women in particular are being brought from poor parts of the world to this country to work as slave labour.

They are housed in cramped and squalid conditions and set to work by those who control them in warehouses and nail bars, for minimum wages, which will be seized for rent anyway.

I met one when I went with police to break into a house where cannabis was growing. He was the ‘gardener’, caring for the plants. He had been trafficked from North Africa.

Why do they put up with it?

The reason is fear. They fear what may happen to them or their relatives if they do not co-operate. And awful though their living conditions are, they may be worse where they come from and they fear being sent home.

They were often tricked into coming here with the idea of a better life. Trafficking is very cruel.

The police have a duty to find the modern slave owners and traffickers and bring them to justice.

But they need help finding them. Where are people living? Where are they working?

In other words, we must all be vigilant, thinking more carefully about what we see going on around us. Modern slavery may be hidden, but it is hidden in plain sight.