When I got my plot, (10 years ago this year!) one side of the plot approx 6 feet wide and running down the whole length of the plot was absolutely choking with it. It obviously hadn't been touched in years. A couple had been given the plot earlier in the year but gave up, beaten and dejected.
You could not use a spade or fork to get into the ground, it was that dense, so I used an axe and chopped the ground into approx 1 foot squares turning the large sods and letting the sun dry out the roots. Took me nearly 12 months to clear. Now I fork it out as and when it encroaches, dry it, and burn it.
A new plot is always hard work and takes time to sort out, the results however are worth all the aches and pains.