Are these the first fruits on the plant, i.e., has it just started setting fruit? Is it all the fruit or just some? Any strange symptoms on any of the foliage?

The plant started setting fruit about a month ago. There are plenty of unaffected tomatoes, it's just the ones that started fruiting a week or two ago, which leads me to believe its weather related or perhaps something in the soil.

The leaves near the affected fruit are a light green/slightly yellow. The rest of the plant is fine. Any thoughts?

Thanks for the response. It is much appreciated. I have noticed that the plant in question is subjected to more shade than the other tomatoes (same variety) in the same bed. I'm lead to believe this is the cause of the deformation. The flower heads on the particular plant in question look quite different to the rest that I am growing. I can supply a picture if needed

Gorbelly's comment made me think that perhaps they aren't getting fertilized properly. If you have an electric toothbrush, you could buzz the flowers (wrap the toofie brush in plastic wrap first if it's your only one. I always manage to get pollen on mine, and it doesn't look very appetizing afterwards!) are self-pollenating, so they don't need bees, but they probably need a little air circulation.

It would be interesting to see a pic of the flowers.

Linda

Yes, a pic of the flowers/buds would be helpful, as "quite different" is slightly worrying.