Suddenly we have to hold two entirely contradictory thoughts in our head at the same time. For the McCanns have now either suffered the cruellest fate imaginable – not only to have innocently lost their beloved daughter but also to have been publicly accused of a wicked crime – or they are guilty of the most elaborate and heinous confidence trick in history, deceitfully winning the trust and sympathy of the world’s media, a British prime minister, the wife of the American president and even the Pope, to say nothing of international public opinion. One of those statements, both of them extraordinary, describes the truth. As a senior tabloid journalist put it to me yesterday: “They’re either the victims of a horrible smear which they will never fully escape or they are cold, psychotic killers” responsible for the death of their own child.

The world’s first seven-sided coins started appearing in Britain’s purses and cash registers on October 14 1969 – strange, alien lumps of cupro-nickel alloy that were greeted with instant suspicion. Bus conductors and Tory MPs fretted that the new 50 pence piece would be mistaken for the old half-crown, causing chaos. Secret documents released years later showed that the Decimal Currency Board – the body charged with decimalising the country by February 1971 – was terrified that the Queen might die before the changeover was complete, forcing it to introduce a whole new set of coins. And according to the BBC, a retired army colonel named Essex Moorcroft founded an organisation called the Anti-Heptagonists, dedicated to eradicating the new 50p on the grounds that it was “ugly” and “an insult to our sovereign, whose image it bears.”

‘These 9/11 truth campaigners merely add a supposedly scientific gloss to already existing conspiracy theories, trying to make the ridiculous seem respectable. In the process, they actually do a disservice to “historical truth”. History gets reduced to a mysterious force beyond our control, and politics – real politics – is imagined to be the preserve of unknown, faceless puppet-masters whom we can never hope to influence. And the rest of us are reduced to the status of helpless spectators, searching amid the rubble of 9/11 and the aftermath of 7/7 for signs of truth and meaning.’

‘Fat is the bane of flushers’ lives. Millions of litres, from half-eaten breakfast dishes, chip-laden frying pans or fast-food joints, are tipped into sinks each day. Eventually they find their way into the sewers. They represent the effluence of affluence. They are the graffiti that the contemporary leisurepolis scrawls on subterranean environments. Thirty years ago the Thames, unloved and abandoned, created few problems for flushers; now, the river’s banks are congested with clubs, boozy eateries and art-complex gallery cafés, all of them disgorging fat.

I wade through some of it at Victoria Embankment. It is at once crunchy and spongy, like putrid bran. Brown and white and grey: a pigeon-shit potage sprinkled with an extra top layer of mop heads and tampons. Flushers tell stories of accidentally getting a gobful of the sewer flies that feed on the fat or of metal grating giving way so that they fall into eight-feet-deep fat-quicksands; the mouthfuls of the stuff they swallow leave their guts raw and hollering for months on end.

But it’s the bouquet that makes their flesh crawl: “You smell it initially. You breathe it all day long. You pass wind and what comes out is the smell of the fat. You can go home and shower as much you like – even with washing-up liquid – but at the end of the day you’re still farting the smell of rancid fat. My wife’ll say: ‘Oh, I see you’ve been sorting fat problems out?'”‘