For a payback scheme to hold up, the amount you'd need to pay back needs to have been made clear to you before hand.
If you haven't had a letter or been given a maternity policy clearly setting out what you will have to pay back if you don't return for the 13 weeks, then they won't be able to claim it back.
If they had made it clear beforehand, the most they could claim back from you is the difference between the occupational scheme and basic statutory entitlement, so 6 weeks at 90% salary then the basic rate of SMP.
I'm currently on maternity leave and hoping for advice. I'm thinking of applying for another job which would start in September. However, I'm not due to go back to work until July (just before school holidays). Therefore I will not have completed 13 weeks necessary and would have to pay back some maternity pay. The surrey scheme is different to the national scheme. I got the first 18 weeks on full pay, and the next 18 on smp.
If I didn't go back, would I owe the whole of the first 18 weeks of mat pay?