I got rid of one by cutting it to ground level, watching out for shoots and snipping them off. The plant eventually gets exhausted. It was sneaking under next door's fence, but it gave up in the end. The reddish brown suckers are easy enough to spot if that's happening in your garden too. It's a PITA but there are many worse weeds.
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The plain green leaves with the pink flowers, looks like a Spirea.
When you don't even know who's in the team
S.Yorkshire/Derbyshire border
https://www.google.com/search?q=spiraea+douglasii&client=firefox-b-d&source=lnms&tbm=isch&sa=X&ved=2ahUKEwi26NTzj-7qAhVfQUEAHS7uCh4Q_AUoAXoECBwQAw&biw=1920&bih=938
"We don't stop playing because we grow old; we grow old because we stop playing." - George Bernard Shaw