Most tomatoes ripen from the inside out, hence the tomato seeds are green because they contain chlorophyll, the pigment in plants which gives them a green hue. Chlorophyll allows plants to absorb energy from light in a process called photosynthesis. As the seeds mature, the outer layer hardens to protect the interior embryo. The seeds also turn beige or off white color when they are ripe. So, a green interior may be green seeds. In other words, the tomato may not be ripe yet. This is the simplest explanation when a tomato is red but green inside; the tomato is not ripe inside.

Another reason for red tomatoes that are green inside may be stress. Stress can be attributed to many things or a combination. Long periods of dry spells, especially when followed by heavy rain or excessive heat over an extended period of time, can greatly affect tomato production and maturation. In these cases, the nutrition the plant needs isn’t properly getting transferred within the plant. The end result may be a tough, green to greenish-white inner core with pale fruit walls and green seeds and cavities.
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Many thanks for that thorough explanation, temperature has been difficult to keep stable, the thing is the Cristal F1 growing next to the Shirleys are OK, once again many thanks