preparing a small area for covering with bark chips etc

I’d use a more natural environmental weedkiller, such as a mixture of white vinegar and salt.
Both can be bought cheaply in volume, using dishwasher salt or path salt.

Landscape fabric like Terram underneath the bark chippings should do the trick.

White vinegar (an acid) and salt can upset the natural microbes in the soil as weedkiller can do.
As merlotgran says, landscape fabric is all that's needed.

An alternative to landscape fabric is layers of cardboard and newspaper, covered with the chippings. It will gradually decompose, but by then, the perennial weeds will have been smothered.

Ooh how did you manage to cut the pampas down? I have a horrible one that looks at me and gets bigger.....

Any kind of membrane laid over the area will work much better than any weedkillers or salt/bleach etc and it won't harm wildlife and micro organisms either. The thicker the membrane, the more effective it will be.

Thanks - now looking for Terram or similar online.
midgey - it wasn't easy! I had looked it up on the net and most say the only way is to get a mechanical digger in to dig it up by the roots. But we have no access here.
So we got covered up, leaves are sharp, and cut the stems back - they're quite soft - a few at a time. Then took to the recycling centre.
You might need to cover your eyes too.

this is one of the videos I found:
www.youtube.com/watch?v=OsAM6MvEyNA&pbjreload=101
Good to see the young lads taking part.

I remembered last night that the last owner of this house left an old carpet in the loft, so I'll use a bit of that. The mice have been at it,but that doesn't matter.
I didn't realise we had mice

Old carpet is even better Fennel; heavy enough not to need to be weighted down into place and is porous to allow the rain to drain through. And you're recycling too! Win win.

I think that depends on whether the carpet is all natural fibres.