Diamond Back Moth

Has any one had any of these pests in their garden yet? I heard about them on the news today. So not only do the poor brassica growers have to worry about Cabbage Whites but now these beasties have blown in from the continent.
Cacoethes: An irresistible urge to do something inadvisable
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I spotted a lot of small brown moths fluttering over my brassicas on Saturday. Then I heard about the Diamondback and, sure enough, that's what I have got. They're not very big, but there's lots of them. I've read that pyrethroids and pyrethrin are effective. These are found in Ant Killers in powdered form. Effective against cabbage root fly. I would like to know if they can still be purchased in liquid form. I think they were banned for general use. They are not persistent and originally derived from chrysanthemums. I think the powder would bung up the sprayer nozzle if you tried to mix it with water. I may try washing-up liquid very diluted in water. This drowns the caterpillars by reducing the surface tension of the water thereby enabling it to penetrate the hairs of the caterpillar and completely coating it, blocking the breathing pores. Very effective against aphids but a pain to spray as you've got to cover all the pests which means undersides of all leaves as well. Won't get right into sprouts etc.My fear is that the caterpillars will get right into the broccoli/cauli/sprouts and ruin the end crop. If anyone has any other ideas I would love to know.
I'm in Belgium and have neither heard of nor seen these moths here - yet! I have enough bother with slugs and cabbage whites without wishing for more pests.
If they come I'll happily squish and drown and sacrifice the brassicas. Don't want to use chemicals as there are so many birds in my garden feeding their young on juicy pests like caterpillars and aphids.
"We don't stop playing because we grow old; we grow old because we stop playing." - George Bernard Shaw
https://www.researchgate.net/profile/Elvis_Asare-Bediako2/publication/43047405_Control_of_Diamondback_Moth_Plutella_xylostella_on_Cabbage_Brassica_oleracea_var_capitata_using_Intercropping_with_Non-Host_Crops/links/551968db0cf2d241f3566ca3.pdf?origin=publication_detail
If you live in Derbyshire, as I do.