The suggestion of the problem is from my daughter in California who is a Landscape architect so probably not her forte.

It looks as though they are in pots. Are the pots big enough? Are they getting enough light, water, nutrients on a regular basis? There are lots of viruses that attack tomatoes. There are also many varieties that have immunity to some viruses. What variety is the tomatoes (F1s)? Root knot nematodes is not a problem that I have ever come across.

I'd not heard of it but had a Google. Can't see if those toms are in pots but if you used fresh compost it can't be that? They look as though they're going to produce so not all bad. You can check the roots once they're finished for the galls on the roots & take the appropriate actions

All in pots, the same size as I’ve always used. They’re Costoluto Fiorentino, which were superb last year. Big and ugly but tasted really good and couldn’t wait to set more this year. Wish I could show you the photo of them.

Just post a photo in your photo area

I think you're worrying too much. They look okay to me. Have you taken some of the top leaves off?
Don't forget they're a sort of heritage variety so they've not been refined to be consistent or pretty. Most of mine had ugly, crinkled leaves that were growing downwards. One out of my four has stems that are two thumbs thick (note to self: keep seed from that one) but the others are just fairly sturdy.
I'm thinking about thinning the crop though...

Have taken nothing off. The main stem has just ended at a height of just 2 ft, in a flurry of strange trusses. But I’ll keep you updated on the conclusion.
Sounds as if yours are good D. I really hope so.

Now understand we don’t have root knot nematodes in this country.