Strength, persistence and attention to detail - it can be dug out, it's just not easy, you end up with very deep holes to get out all the roots and runners.

failing that you could try a glycophospate based weedkiller when new growth starts. Not that environmentally friendly but used sparingly is ok.

Good luck!
I don't want to kill ours, just contain it. I had some 600mm wide , 10mm thick industrial plastic sheeting, so I dug, scratched & scraped to put it in as a block. I then destroyed half the lawn removing all traces of runners, roots etc. Clearly 600mm down wasn't enough, as it has come back! I may have given it the hump a bit, as last summer for the first time it came up the other side of our dry stone wall!!