WE shall call him Billy, because we do not know his name, where he came from, or where he was headed. All we know is that he is London’s most unusual tourist of the winter, and that his visit may end in tragedy.

Billy is a rare northern bottle-nosed whale, and to whales rivers are like tunnels. He was spotted making his way up the Thames yesterday morning, progressing slowly under Tower Bridge. You had the overwhelming feeling that he did not want, nor intend, to be there. Billy had almost certainly taken the wrong turning.

He kept his great shiny black bulk, at least 12ft long, and weighing an estimated six tonnes, submerged, surfacing every minute or two to send a puff of spume from his blowhole with an odorable snot, and arching his back like a dolphin to afford a glimpse of his dark triangular dorsal fin.

All morning he swam slowly up stream, and as television and radio spread the word of his arrival, increasing numbers of Londoners began to line both sides of the river.

Two police boats and a rescue launch tracked Billy’s progress at a respectful distance; he would have been capable of capsizing them. Slowly he made his way upstream against the falling tide.

Billy appeared to take no interest in the capital’s sights. As he approached Lambeth Bridge he ignored the offices of the International Fund For Animal Welfare on his left; more understandably he swam straight past the building that houses the London office of the International Whaling Commission.

He paid equally scant attention to the Tate Gallery; its current attraction is an exhibition of Toulouse-Lautrec, who did not paint whales.

Then Billy had a change of mind. Clearly disorientated, he turned and swam close to the South Bank, the escort boats dutifully following him. But he then took a firm decision to head upstream at a suddenly increased pace. The crowds on either bank became bigger by the minute as office workers left their desks for a closer look.

Even staff at the MI6 headquarters by Vauxhall Bridge took a break from spying to gather on their balcony. Some onlookers, rather pointlessly, even waved at Billy. Soon he was surrounded by a wheeling flock of seagulls and, at much greater height, two television helicopters.

Shortly before 1pm one of the police launches turned about and headed rapidly back downstream, probably because it was lunchtime. It was replaced by another rescue boat and shortly thereafter by the launch of the Port of London Authority harbour manager, anxious to see this rare foreign visitor on his patch.

Billy ploughed on through Pimlico, past the closed-down Villa Elephant riverside restaurant and the flats of Dolphin Square. Neither interested him.

As he approached Battersea power station with the tide almost at its lowest, he suddenly found himself beached, immobilised with almost a third of him out of the water. He appeared distressed, arching his back and flailing his huge black tail.

Three workers in luminous yellow jackets saw his plight, went to the water’s edge, and splashed at him. After a few moments of further desperate wriggling Billy freed himself and rewarded his rescuers with a good soaking from his highly relieved blowhole. On the Chelsea Embankment, there were by now many hundreds of sightseers lining the river.

As Billy passed slowly under Chelsea Bridge he looked all set to make for the head of navigation at Teddington Lock, until he took another wrong turning. Swimming close to the north bank he approached Cadogan Pier and headed into a dead end between the embankment and a pontoon of moored boats. He was virtually trapped.

Enter the heroes of the hour. Edwin Timewell, a volunteer whale conservator who had come to watch after hearing about Billy on the radio, waded waist deep into the muddy water, closely followed by Bettayeb Fethi, another bystander. The two men splashed water on Billy, nudged him gently, and freed him from the rope.

“He is a beautiful creature, and it was such a thrill to be so close to him, but I fear there is a high chance he will die,” Mr Timewell, 37, said. “He is clearly lost.”

To the concern of the hundreds watching, Billy then disappeared. Even the escort boats seemed briefly to have lost him. It was by now midafternoon with only two hours of daylight left. If only he would head back towards Southend and the open sea.

After several anxious minutes Billy reappeared. A relieved woman suddenly announced to anyone who would listen: “I’ve just phoned my son in Saudi Arabia, and he says the last sighting of a whale in the Thames was in 1913.”

In those few minutes something had happened to Billy. He seemed to have lost the will to head upstream. Instead, worryingly, he swam slowly in circles in midstream, emerging every minute or two for a little blow and a flash of his dorsal.

As daylight faded there was no immediate prospect of persuading Billy back to the sea. It may have been coincidence, but as whales are highly intelligent creatures, it may not. As he circled in his confusion he was overlooked by the Battersea Park shrine to Buddha, whose followers believe in the sanctity of the life of all the earth’s creatures, great or small.

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