The "little black bits" is probably caterpillar poo, and the caterpillars could be the tomato moth larvae. This is the chance you take growing tomatoes outside as they are more free to lay their eggs as opposed to a greenhouse with limited entry. Apart from removing the infected fruit and feeding them to the birds, this is an added advantages as birds prefer caterpillars to tomatoes and will hopefully leave your tomatoes alone. Apart from using a chemical insecticide, which you obviously don't want to use on edible plants, and I don't know of any organic methods, there's not much else you can do except to shake the plants to dislodge them and squash them. Having said that, I have heard that a salt solution sprayed onto the plants works, but I can't confirm this.

Thank you Myron for your helpful comments. I have picked off more caterpillars tonight and have rescued some of the larger fruits and placed them with a banana to ripen, on a sunny windowsill.

Having grown container tomatoes for several years without any problems, this was a "first" for me and quite a shock too to see so many holes in the fruit. We only have a small patio garden at the back of the house, with a very narrow border for roses (the front is larger but given over to flowers and a lawn) so a greenhouse is out of the question, unfortunately, and hubby has his potato barrels and I also have other container fruits. i will continue to gently shake the plants to dislodge any more caterpillars that might be hiding in the plants and squishy squash them underfoot. So grateful for your helpful advice.