Mulch has very little effect on perennial deep rooted weeds, sadly. It does help keep seed weeds down and the roots of things like couch do come to the surface and are easier to remove, but Bindweed, ground elder etc will grow through it.

Ah bindweed, the dreaded "devil's guts" - roots can go down six feet deep and impossible to dig out. One solution is to allow it to grow and train it up canes. When its a couple of feet or so feet high protect surrounding plants by spreading plastic over them, lay the canes flat, then use weedkiller on them. It takes several years of consistent treatment but it does work. Can't remember where I picked up this trick but it was effective and reduced an enthusiastic infestation quite radically.

Thanks Owdboddy and Stera, I'm beginning to realize there is no easy answer to the problem. I will grow the bindweed up canes though.

Bark chippings may look great to start with, but we have to remember that they soon rot down and so form a natural seed bed and it's not long before all sorts of weed seeds set in, yes you can get different grades of bark and if it has to be used then the thick pine grade is by far the best, as regards the bind weed, then the only real way of dealing with it is to dig it out, then keep digging as it comes back, eventually you will win he battle, but you have to put the effort in, far better than trying to hide it under bark.

Julien I had actually almost won with the canes method but then we moved house and the new owners weren't gardeners, so it was probably a waste of effort all along. I failed totally with digging it out - the roots were very deep and spread all across the bed. As you say its persistence that counts - try both methods!