Practically speaking at 154E per week 8k per annum you are not even using up your personal credits so the OPF tax credit is doing you no good. If you start earning above 16,500e per year then you will be using up your full personal tax credits. Removing your OPF tax credit on this basis won't cost you a penny and may save him a fair amount of money. If I were you I would sit down with his advisor and get the full picture. As a whole its best off if as parents you both have more money and is best to find out the optimum solution for your joint circumstances. Just make sure social welfare OPF doesn't come into it. It would also be worth ensuring that he indemnify you from any tax costs and that going forward he doesn't claim the marriage credit from 2017 on! You can then negotiate and agree a position each year there after based on your earnings and his. I honestly think that would be a fair settlement.