Just had a look at the usual suppliers ( Screwfix, Toolstation) and it seems that only water-based woodworm treatments are now available from them. My local Robert Dyas shop did not have any Rentokil woodworm treatment on its shelves, and a brief on-line search indicated that most suppliers are showing "out of stock". I did eventually find Rentokil's web pages with product information, from which it appears that the domestic stuff is also water-based now, although both solvent-based and water-based products exist for professional use.
http://www.rentokil.com.jm/about-rentokil/sds/ woodworm at end of list.
Looks like in future the DIY-er may have to rely on traditional treatments such as paraffin for treating traditional plywood. I note that the packaging of some of the current products refers to the product being suitable for treating floorboards and "traditional" furniture, and the picture on the tin shows traditional solid wood (not plywood) furniture being treated. I haven't actually seen any warning advising against the use of water-based products on plywood, but my experience with pre-war plywood is that getting it thoroughly soaked with water is definitely not a good idea, and a thorough soaking would be essential to penetrate deep into the wood.