I would say that Gooseberry Sawfly is the problem. You could use something like soapy water, neem oil or pyrethrum. Do your best to pick them off by hand as well. There are systemic chemicals like Sprayday (banned) for fruit but you would probably have to wait some time before harvesting; something you would need to check up.

yes they will be sawfly larvae.
if you can pick them off by hand and offer them up to the birds/pond fish if you have any. The green stuff sounds like frass [their poo].
if you can, avoid chemical sprays much better for the environment. The fruit will still develop and can be harvested as normal.

Thank you both for your help. We have spent an afternoon picking caterpillars and cutting off nibbled leaves and 'dirty' leaves....beats watching tv. lol.

Try to think of it as a kind of meditation...not that I always manage that! :)

Once the caterpillars have been removed, feed the bushes with a high nitrogen feed to stimulate new leaf growth.

I hope you can get rid of all of them. If they are not removed they can strip the bush in just a few days. (Surprisingly this doesn't seem to kill the bush!)Warning: They overwinter in the soil under the bush. I hit on the idea of putting a piece of old pond liner round the bush so they couldn't get out in the Spring and had no more trouble until I moved the bush and forgot the plastic - back they came!