Posted: 04/05/2012 at 16:02
We had this in our last house. Glyphosate, and lots of it, is the only answer! I found spraying with a stronger than normal solution to be fine, but it took about three years to kill it all. Do not dig it up as you have to dispose of at a licensed site as it is notifiable.
Be aware that it can damage house foundations, so if you're thinking of selling you need to make sure you don't have any within two metres of your property or your buyer may not be able to get a mortgage according to a suyveyor I know!