If you just warn people, they often simply ignore you. But if you ask them a question, then they have to think about it. And once they start to think about the consequences, they almost always calm down. Unless they're drunk, of course. Or stoned. Or aged between fourteen and twenty-one. Or Glaswegian.

Not being invited in is one of the boxes on the “suspicious behavior” bingo form that every copper carries around in their head along with “stupidly overpowerful dog” and being too quick to supply an alibi. Fill all the boxes and you too could win an all-­expenses-paid visit to your local police station.

Carved above the lintel were the words SCIENTIA POTESTAS EST. Science points east, I wondered? Science is portentous, yes? Science protests too much. Scientific potatoes rule. Had I stumbled on the lair of dangerous plant geneticists?

The motto of West African cooking is that if the food doesn't set fire to the tablecloth the cook is being stingy with the pepper.

It's a police mantra that all members of the public are guilty of something, but some members of the public are more guilty than others.

The general public have a warped view of the speed at which an investigation proceeds. They like to imagine tense conversations going on behind the venetian blinds and unshaven, but ruggedly handsome, detectives working themselves with single-minded devotion into the bottle and marital breakdown. The truth is that at the end of the day, unless you've generated some sort of lead, you go home and get on with the important things in life - like drinking and sleeping, and if you're lucky, a relationship with the gender and sexual orientation of your choice.

If you just warn people, they often simply ignore you. But if you ask them a question, then they have to think about it. And once they start to think about the consequences, they almost always calm down. Unless they're drunk, of course. Or stoned. Or aged between fourteen and twenty-one. Or Glaswegian.