Along the river from Henry the Eighth’s palace at Hampton Court, west of London, there’s a huge area of water works, a purification facility built in the 1850s. Some of it is no longer in use, in fact some of the buildings are being restored and converted. One of the huge pools is now dry – and growing there is pampas-grass, Cortaderia selloana. Just one plant.

I first spotted pampas-grass here two or three years ago, in fact there were a few plants scattered across the area. Then they disappeared, there was no sign of them for a couple of years. Perhaps, afraid they might become invasive, the water company dug them up – though it seems unlikely they would have bothered.

Then, driving by in October on the way to the attractive Walled Garden at Sunbury, I spotted this one plant (above, click to enlarge). It looks wonderful set against a fat clump of brambles, but I wonder how long it will remain?

Pampas-grass was first grown in Britain in 1848 and was first seen in the wild in 1925. Mostly, it’s plants thrown out of gardens that become established in the wild but this one looks as if it’s grown from wind-carried seed. You can see how it has become established more widely on this map produced by the Botanical Society of the British Isles. It's invasive in parts of the USA, especially California.

Then, a few days ago, I came across a piece in Britain’s Independent newspaper that made me see pampas-grass in a whole new light. Growing pampas-grass, it seems, is a sign of swinging. (There will be no photograph to illustrate this.) The Independent reported that “Mariella Frostrup, the television and radio presenter, had received unwanted attention by placing a pair of pampas grass plants on the balcony of her Notting Hill flat. "Who knew," she wrote on Twitter afterwards, "that pampas grass plants are a signal to fellow swingers?"

“Fellow broadcaster Esther Rantzen received similar publicity last year when she revealed how she removed the plant from her own garden after discovering the supposed connection with swinging. "There's an awful lot of pampas grass in Luton," she observed of the town which had recently failed to elect her as Member of Parliament.”

So, be sure you know what you’re doing before planting pampas-grass where it can be seen by passers by.