I meant to give you regular updates on this but things have not quite gone as planned.
First, one of the cats was digging up the surrounding earth to use as a litterbox and tearing at the fleece and the cellophane cover. I started covering the plants with the offcuts from the hawthorn at the bottom of the garden (which I still haven't been able to throw out as my next-door-neighbour's builders haven't returned to empty my garden waste bin which they filled with rubble) as I thought the thorns might keep furry bottoms out of my salad. Eventually it worked though I have noticed Professor McTufty (one of the feline visitors to the garden) is still sniffing around the area.
Unfortunately that has not been the end of it as, lacking the protection of the cellophane tunnel, the leaves have now provided a delicious meal for every slug and snail in the garden.
I may well have to start again with a new seed roll and anti-cat measures from the start but I'm a little disheartened and I wonder whether it's worth it.