In your case, how about
removing the gravel - placing a barrier on the ground, such as black
polyethene and then placing gravel back on top?

I removed some of the gravel and there's black polythene under it.
Underneath the polythene is riddled with the weeds roots which I'll have
to dig out as much as I can before laying some new polythene.

The weed have grown up through the polythene.

It would be nice to find a easier fix but I don't there is one after
some initial research.

Thanks for replying.

Phil