Congrats!! If you were technically pregnant when you started the job then you won't get SMP. But assuming you've worked and earn enough then you'll be eligible for maternity allowance. Thats £180ish a week for 39 weeks. Then you're still entitled to leave until you've been away for 52 weeks but it's unpaid. It's unlikely you'll qualify for any enhanced maternity pay from your company but it's always worth asking. They entirely set the rules on that stuff and can set the criteria for almost whatever they like. My company for example gives differing amounts depending on whether you've been there 1, 3 or 5+ years.
You’re eligibility for maternity LEAVE (52 weeks off work), you might not be eligible for SMP (statutory maternity pay (90% pay for 6 weeks followed by £185ish a week). If you were pregnant (even if you didn’t know yet) when you started with that employer then you won’t be eligible for SMP. BUT you will likely be eligible for maternity ALLOWANCE from the government at £185ish a week from when you are something like 28 weeks pregnant - you don’t have to wait until the baby is born so you can claim early if you want to save up a bit and will have no other income. Do you get any OCCUPATIONAL maternity pay? (CAPS for all the terms as it is confusing!) And congratulations!