Your work should have a maternity policy might not be in your contract. It's often 13 weeks.
I didn’t return to my teaching job after having my first daughter. I had to pay back my occupational maternity pay, which was around £2400 (off the top of my head). I agreed a payment plan with them to make it affordable.
You only have to pay some back if you've been getting enhanced mat pay.
I got enhanced mat pay and didn’t have to pay anything back - so it varies depending on your workplace. I emailed HR when I wasn’t sure to ask these questions as they have to keep it confidential.
My company I have to go back for 6 months or pay back the enhanced pay not sure how much it will work out but I do sometimes consider it.
If you only receive SMP then you don’t pay anything back Anything extra you may need to pay back If your contract doesn’t say anything (and no policies etc around it) I’d assume you don’t need to :)