Posted: 27/05/2017 at 09:37
I don't think there's is an easy way other than as Punkdoc says lots of physical hard work - digging it all out and making sure you get all the roots out as it will regenerate from the tiniest piece. I think there was a piece on GW about this some weeks ago, Jo Swift visiting a garden and discussing how it has become a severe problem is some areas of the country as it's spreading into our waterways and destroying native habitats.
Link below to some advice, first bit is aimed at habitat control. Lower down has suggestions on removal methods - good luck