I think you are wise to go for a walk-in type. You can buy them but they're pricey. I know someone who bought a load of fishing net (the one thatchers use) He built a wooden frame from treated roof battons and used stainless staples to secure it.

Thanks Heron - d'you happen to know the size of the holes in the fishing net?

You'll need half inch mesh, because anything bigger allows in them pesky cabbage whites. Bear in mind, too, that small whites drop their eggs, so you might need fleece over the brassicas if you really want to protect them fully. Phil J

I still find the butterflies get through 1/2 " mesh I have it on the fruit cage and when i put cabbages in the pesky things got in. The wings are quite flexible. So I have adopted a patrolling method. better still I pay the kids 5p per caterpillar :o)

"drop their eggs" ? They don't give up do they lol The mesh on thatched roofs is also about 1/2 an inch but I would not look for anything less as it may not let enough light in.

Thanks very much to everyone who responded. Will try the 1/2 inch mesh and be on the look out for dropped eggs!

they normally 'glue' their eggs to the underside of the leaf. so when you see them flying, inspect the undersides. the eggs are yellow and thin barrelled shape .about 1-1.5 mm long