They are being overtaken by some pest. The Missus thinks it's only caterpillars but I suspect it's also something else.

TIA

mate,you have leaf miners, tiny maggot like grub inside the leaf. You can spray neem oil over the leaves and around the base of the plants to control them(they are laid) but you need to remove the infected leaves as well, just pinch then off. You can also ask your local gardening supply shop for a treatment as well as I dont know what they have here to treat them.

A spray of Cypermethrin mixed with Abamectin will kill the leaf miner infesting your tomatoes.

Do not over apply; follow quantities given on the bottles. Wear protection, need more than one application and you must spray the ground under your plants as well.

A slower but healthier choice is to apply neem oil mixed with detergent. It works but it's not instant.

Finally the plants do not have much more life left in them, by June the rain will do them in. Doing nothing is also an option.

Many thanks. The wife has been duly informed.

Now I just hope for a few home grown tomatoes. She has a job in front of her to remove all the infected leaves but she says she'll take care of it right away.