Thank you for confirming.
The difficulty is that you both own the savings equally. There is no separation of assets under marriage law in England and Wales.
So dividing it into your half and his half is a little arbitrary.
In a divorce, the court could only divide what is left in the pot.
If you could show that he had been reckless though, with a spending habit, you could argue to retain your share of the savings that are left over if he has spent all of his 'share'.
It would depend on the view of the judge as to what the outcome would be.
There's really no legally binding contract you could make that would protect you in this situation - pre-nuptial and post-nuptial settlements are not binding under UK law as the law stands today.
You could write a short agreement that you both sign to the effect that he is taking responsibility for his share and won't claim on your share, but it won't be binding in a divorce unless the judge feels that it is fair in all of the circumstances.
I hope that this clarifies the law for you? Can I assist further?