Books and newspapers are filled with news and debate about crime. As far as I can tell from the evidence, crime in the UK peaked in 1995, dropped sharply up to 2000 and has dropped more slowly since. There are variations for individual categories of crime, and the whole business is complicated by changes in the way recorded crimes are counted, but the overall trend is clear.

This might give pause for thought to those who give the credit to Labour’s increasingly authoritarian laws. It normally takes a year or two from a measure being introduced in Parliament to it having an effect on the streets. If government law and order policies have made the difference, we would have to conclude that John Major gets the credit: whatever his Government did in the early ’90s must have done the trick. Blair, by contrast, appears to have managed to slow the fall: any new policies introduced around 1997 and 1998 would have started making a difference around 2000, at just the time the drop in crime petered out.

As it happens, I don’t think the evidence supports the law and order policies of either party making much difference. The economic upturn of the early ’90s probably had a much bigger effect. ASBOs, CCTV, high prison populations and rafts of draconian measures brought in or accelerated over the last decade seem to have made little or no difference.

But is there a link we’re missing? Figuring out why crime falls and rises isn’t simple. After all, if it were just a reflection of the economic state of the nation, why was crime so much higher in the 1980s than the 1970s?

I’ll admit that I really don’t know, but take some consolation from the experts not knowing (or, at least, not agreeing) either.

Which brings us onto David Steel as our modern saviour, a secular deity perhaps. Did Sir David deliver us from evil more effectively than the church has ever managed?

You’ll have heard of, or read, Freakonomics by Steven Levitt, an American economist. It’s a cool, trendy book which claims to sift through the data and find new links, new explanations that overturn the boring old orthodoxies of social science. One of the most well known claims in Freakonomics is that the fall in crime seen in the US (similar to the fall in the UK, but slightly earlier) resulted from legalised abortion.

The argument goes like this: abortion was legalised in the US from the late 1960s, with Roe vs. Wade legalising it across the country in 1973. After legalisation, the foetesus aborted were disproportionately from poor families: just the sort of background most likely to produce criminals.

Fast forward twenty years to the late ’80s and early ’90s and crime across the US mysteriously starts falling – something predicted by few experts and explained by none. Levitt’s explanation is simple: crime fell because a lot of the people who would have been criminals (mostly men in their late teens and early twenties from poor backgrounds) were aborted and are thus finding it a lot trickier to rob, burgle, rape and murder.

Levitt is good at giving conclusions, rather less so at giving us the information we need to check them, but we can see if the theory holds true in the UK. Statistics on legal abortions can be found here, and crime statistics here (look at pages 18 and 19 in the PDF).

Legal abortions increase rapidly from 1967 to 1971, then stay roughly the same throughout the 1970s. On this basis, I’d expect to see a big drop in UK crime in the dying days of the Thatcher Government, but it didn’t happen: crime continued to rise until the mid-90s when those early aborted foetuses would have been in their mid-twenties and probably settling down to family life.

There could be a more complex link of course, but the simplistic and strong link Levitt claims to have found in the US doesn’t appear to hold true in the UK, so it’s with some sadness that I have to put my plans to found a religious cult worshipping Sir David on hold.

Does the whole business tell us anything useful? I think it does, but as a warning rather than an answer. Be very wary of anyone claiming that society is collapsing under the weight of crime, as a certain Mr Cameron has suggested. But also be wary of people claiming to know why crime levels are rising or falling: check their claims and the data they’re based on very carefully.

And if anyone does figure it out, please let me know.

* Iain Roberts is a Lib Dem member living in Cheadle.