I really didn't know that I was pregnant when I started my job. You have to have worked for the company at least one week before you got pregnant to qualify for SMP from the employer, but the pay and the leave are entirely different things, maternity leave can be anything between 2 and 26 weeks long, (longer if you'd worked for the company longer) when you tell you're employer that you're pregnant they will have to give a form telling you why you are not entilted to SMP. You need to send that form along with an MA1 and your matb1 certificate to the job centre with some of your payslips and they will work out how much Maternity Allowance you're entitled to, it's currently �117 a week or 90% or your weekly wage whichever is less! if you need anymore help, all this info is on the DWP website.
Good luck and congratulations!!
k8.x