I don't know what is available in the UK. Here in the US, I use permethrin. They also make it for spraying on clothing as a deterrent.
https://www.amazon.com/s?k=permetherin+spray&hvadid=77996658719259&hvbmt=be&hvdev=c&hvqmt=e&tag=mh0b-20&ref=pd_sl_326dfnurgi_e
If you can find something like it...