[whitespirit66]

Now that I seem to have got on top of the slug and snail problem, something else is attacking my lettuces (Webbs Wonderful).

The outer leaves have small holes all over them, and look like doilies. THere also seem to be a lot of flies near them, but this could be because of my using industrial quantities of Doff and the numerous slug bodies attracting flies.

Apart from the holes, I can't see anything else on the leaves apart from the odd small brown patch.

Please advise what my problem is, as I have to throw most of my lovely lettuces away, the inside 'heart' of them is all that's edible. 

[Ice]

Sounds like flea beetle.  If you want to be organic wait for someone else to answer.  I find one dose of Provado Ultimate works a treat.  But don't spray too close to harvest time.