Erm, I'm a bit confused. I can't really understand why you've put a membrane there, I don't see how it helps in terms of pruning back. Whether you use bark or chippings is purely an aesthetic choice, so that's up to you; bark will gradually rot down, chippings will just get dirty and soil will collect in it eventually, but I would just say that collecting the clippings off either of those materials will be no easy task, and natural leaf loss means dead brown leaves will collect there and also be difficult to remove.

I'm presuming that you don't want flowers at the foot of the hedge that risk being trampled on when your trimming the hedge.

It's purely a matter of taste (and cost). Me -I'd chose local pea gravel or something to connect the colours in the house walls. I hate bark chippings - but that's personal choice - but they can be more appropriate if you have something that you might describe as a woodland garden. Whichever you go for you need a good deep layer - 3-4 inches ideally - to reduce weed growth.

Thankyou Bamboo and Urbanite for your reply, its exactly how you say urbanite we keep the area weeded and try not to let flowers root, as they just get troden on and it is also difficult to get under the hedge to remove plants ( we are very mature !! gardeners,so we are trying to reduce the work ),and after 2 hip replacements its no mean feat to get under the hedge.Understand your mention of collecting the dead leaves bamboo,we perhaps need to study the options again to decide which will be best all round for us. Thankyou both.

Just wondering if it might not be easier n the long run to underplant it with some tough ground cover? You wouldn't have the problem of disturbing the gravel/bark when you collect up the trimmings and you could just slice off any that spread too far into the border.

But it's easier to put a tarp/sheet down on top of the bark/stone and collect the cuttings in that as you go.
Another option, would be loose laid paving (ie not cemented) 10(ish) 2ft square slabs would do it with half inch gaps between which you could soften with aubrietia, sedums etc.

This would be give you a firm place to stand for trimming the hedge, add other texture and other colours. I'd still go for paving colours that tie in with the house and local area.

The slabs don't need to be in a straight line, they can be more like stepping stones or you could put in a bit of a curve - lots of ways to add interest and you could stand pots (with plants that want different soil conditions - or herbs for easier picking) on some to add even more variety.

I'd take up the membrane and just use 2-3 inches of mulch (bark or composted materials like animal manure) along the whole length - this will degrade over time, but can be topped up when it needs it, can be stood upon, and a sheet of plastic or a tarpaulin over the top before you start trimming the hedge will catch the clippings. Any natural leaf loss that falls onto the mulch won't be an in issue, it will degrade along with the mulch and get taken into the soil because there's no membrane preventing that. You can gently hoe it over if too many dead leaves are sitting on top to make it look tidier, or simply top it up. 2-3 inches depth will prevent most weed growth, and it will improve the soil no end, without any need for digging. This is assuming you don't have a problem with resilient weeds like bindweed... although even a membrane won't stop most of those, they'll find a way out...