Are they getting enough Sun. They need many hours of Sunshine to ripen.

What direction are they facing?

Its still early, my first this and in past years is 1st july.
the plants and the tomatoes have to be mature before they ripen and I always find its the small bush varieties first, then the modern cherry tomatoes then lastly the moneymaker/ shirley types.. Mine are in cold greenhouses and fedand watered regularly
August is when we get a glut!

It does seem to take for ever doesn't it?
You can help to speed ripening somewhat by putting a ripe tomato near the bottom truss. The gas given off it will help the first ones to ripen. After that always leave a red one on the truss to speed up the rest. A banana or even a banana skin will have a similar effect. (This also works for the green ones you take off at the end of the season)

Steragram what a great tip.