I bought a plot of land that was completely overgrown with Willow and dense
brambles. It had been like that for decades. The plot now has numerous
vegetable patches and lush lawn.
I created a mountain of shredded willow (and wore out an expensive shredder)
and was scratched raw by brambles that were above head height. The veggie
patches were a pain to dig out because of the tangle of willow and bramble
roots, but I've had some excellent crops in my first year. (My neighbour is
an experienced gardener and he was really teed off because my runner & broad
beans and spuds all outperformed his in yield by about 50%!

The grass was sown using Wickes lawn seed last year. I didn't dig out the
bramble roots and just cut off the willows a tad below the surface. Both
Bramble and Willow try to stick out shoots but these are dealt with by the
weekly mow before they get to be noticeable. The Brambles appear to be
giving up after a year of mowing, but there is some evidence that the
willows are tougher - although the odd patch of new toadstools suggests some
of the roots are rotting.