The badger cull: What does the science say?

I have spent a lot of time in the last few days trying to get to grips with the apparently simple question: does the scientific evidence support the Government's proposed cull of badgers as a way of controlling TB in cattle?

It is certainly an important issue - 25,000 cattle were slaughtered for TB control in 2010 and in the last 10 years TB has cost £500 million.

But does science have any answers? Cast your mind back to the crisis over mad cow disease - BSE.

Scientists were asked for advice about whether BSE in cattle could spread to humans.

Back came a pretty clear-cut answer: it is very unlikely.

On the basis of that, politicians assured us all eating burgers was safe and John Gummer, then the agriculture minister, fed one to his daughter on camera.

Sadly the answer was wrong and BSE did spread to humans.

Fortunately, the number of people with CJD - the human equivalent - was small and the epidemic is dying out. But at least there was an answer.

With badgers and TB, science seems to have no clear-cut answers.

There was a trial of culling, which started in 1999 and has been analysed up to 2010.

The figure that comes out of that, is that IF culling is done over a wide area, IF it's done for four years and IF 70% of the badgers are killed, it will reduce TB in cattle by around 16%.

That is what science tells us. The rest is politics. The Government says, yes it is worth it.

In areas with high infection rates, that could make a big difference. And existing control methods won't have the same effect.

But eminent scientists, like Lord John Krebs, who instituted the trial and used to run the Food Standards Agency, says 16% is not worth it.

Lord Bob May, an ex-government Chief Scientific Adviser and former president of the august Royal Society, said culling was not evidence-based policy but policy-based evidence - i.e. that the government was picking and choosing the evidence to fit its argument.

One thing is certain: culling will not wipe out TB in cattle.

Some scientists even doubt that badgers play much of a role in spreading the disease - the Government's advisers say they are thought to be involved in about 50% of outbreaks.

But even if that is true, much of TB is spread among cattle with badgers not playing any role.

In the long run, one solution is the development of better vaccines for badgers and for cattle.

The Government is investing £20 million in that over the next five years. Not enough say the critics and not fast enough.

Time to stop now, my head is beginning to hurt.

Conclusions? My personal thoughts: culling will not reduce TB by much, it will be expensive, it will polarise society, it might leave wounded badgers in pain, and if botched, it either will not work or could endanger whole local populations of badgers.

But none of those thoughts is particularly scientific.