If you have 6 months service by the end of the 15th week of the pregnancy (and have told your employer by this point), you are eligable for company maternity pay:
At present, the statutory requirement is 90% of sal or �112.75per week (whichever is higher) for 6 weeks. �112.75 for a further 33 weeks and 13 unpaid weeks. Total 52 weeks. The company may have more on offer than that, but that is the minimum.
If not, you can apply for maternity benefits from the DSS.
into the 15th week BEFORE your baby is due. Basically you should have been working for your employer when you got pregnant, which is of course 2 weeks before you conceived.