Thanks very much, I shall see what I can find. A fellow allotmenteer may be interested in sharing a large roll of 4mm. I had found 350m of 4mm for £50 near to my location but that’s alot of hoops!!
The black plastic mulch is definitely weakening the rampant horsetail on my plot. However, the sheeting is gonna stay put for a long time yet – trowelling out horsetail where there is no mulch cover is time consuming; mulching makes my plot managable in these early stages 
Best of luck with that bindweed.