There are a lot of factors to consider, and I'm not much of a tortoise sexologist, but could you give some details about your husbandry?
I don't have any information on the breeding cycles of stars in the UK, but I know there are a lot of star keepers there. I would recommend searching for a UK breeder and getting in touch with them.
I have found that keeping a male tortoise by himself for a season helps quite a bit. Set your male up in a new habitat, plenty big enough for him to wander and feel comfortable, and just let him be a tortoise over the winter. Then in the spring, put him in with the girls. I think you'll see that he has become interested.
The UK breeding season is spring summer.
I agree maybe he is a late bloomer, some males are so laid back they may as well be gay too and getting another male would be my choice.
A winter separation is the easiest way to solve this problem. Enclosures that are too small or having them sexes continuously year round creates an over familiarity.
We too have a male star and at first he was very quiet (we obtained him from a friend when he was 6. He's now 7).
We have built him an entire new enclosure with new toys (rocks & hides) bur he has since taken to one of his rocks as a mate which he 'humps' on many an occasion (& more often than not when we're eating or have peeps round)! He h as also become very territorial as he has gotten older too! We too are in the uk and let me tell you, when my Sheldon is in season he paces round the enclosure & humps as though theres no tomorrow and this can be outside of 'our' usual seasons. Only tonight was he humping & pacing! Good luck and keep us informed on as how you get on.