Walk down the streets of Soho in central London and sex is right in your face - strip clubs, porn shops, open doors with handwritten signs saying 'model upstairs'.
We did a bit of secret filming a few days ago, went into a few of the places where the prostitutes hang out. It was three in the afternoon and they were full of men of all ages.
"Hello darling," said the brothel madam. "Come and see the lady for yourself".
The 'lady' came into the bedroom in her underwear, no more than 20 years old.
Her manner was brisk, her accent and appearance somewhere from central or southern Europe. 'Twenty pounds for sex' she said.
We looked at her open mouthed in amazement. Twenty pounds is thirty dollars.
That's the price of a couple of pizzas in London. The police told us later that the women are made to pay rent to their handlers before they make any money of their own.
The calculation is that she would have to have sex with 15 men every week to break even.
Campaigners say that prostitution at that price almost certainly means the woman has been trafficked - you cannot possibly live on an income that low even if you were doing it voluntarily.
Britain has been accused - quite recently - of not taking trafficking seriously.
After all, say the campaigners, it is basically slavery in a modern form, the second biggest organised crime in the world behind drugs and Britain's a favoured target for traffickers.
You would expect Europeans to be victims in a borderless continent, but the two biggest groups are from Nigeria and Vietnam.
Forced labour of Asian men is a huge problem too in underground drugs factories.
But it's becoming clear that gradually that England is starting to take a leading role in getting on top of trafficking.
A police raid, early in the morning, right next to Chelsea's football ground in west London, and out came two Russian women in handcuffs, allegedly part of a bigger and very organised gang bringing women into the UK.
Twenty or thirty officers at various locations doing simultaneous and well organised raids. How many do they do like this? 71 last year, apparently.
That's well over one every week in London alone.
The Home Office (border control, police, immigration) and the Foreign Office are also trying to be more organised up and there's more of a push in tandem with other European police forces to stop the problem at source rather than once it's established here.
It is really difficult though because London's got so many foreigners in it and the trafficking happens in plain sight and on such a massive scale.
You could see that from the place where we found the victims of the traffickers. A house converted into flats on a main thoroughfare, right opposite Earls Court exhibition centre in fashionable west London.
While waiting for the police to bring the women out we did some more maths. Seven women in five flats. Each flat would be rented by the traffickers for about 2500 dollars a month.
That means the traffickers must make $140,000 before they turn a profit on one property alone, and still it is incredibly lucrative.
The police said that Earls Court was full of similar places, so even if you accept they recognise the scale of this even they'd agree that they're far from on top of it. It's slavery, right under the noses of people driving to work and getting on the underground.
A quick plug for some excellent campaigners who have taken an animated film to no fewer than 13 Eastern European countries to warn young women that if it sounds too good to be true it probably is. They're off to Ukraine and Russia next, and they'll have their work cut out too.
Have a look yourself - you'll never trust a man who claims he can get a woman work in Britain again: www.twolittlegirls.org