it depends on: If, by the 15th week before your due date (an important week, also known as your Qualifying Week), you’ve been employed by your present employer for at least 26 weeks (simply put, you’ll probably have been working there since before you conceived) and if you earn above the lower earnings limit for paying National Insurance (this is £84 for the 2006/07 tax year), you can claim SMP.
http://www.supernanny.co.uk/Advice/-...ity-Leave.aspx

Also look at link : http://www.direct.gov.uk/en/Employme...es/DG_10029285

How much SMP you'll get:
If you get SMP, your employer will pay you 90 per cent of your average weekly earnings for the first six weeks, then up to £112.75 for the remaining 33 weeks (or 20 weeks if your expected week of childbirth begins earlier than 1 April 2007). You pay tax and National Insurance in the same way as on your regular wages. Your employer reclaims the majority of SMP from their National Insurance contributions and other payments. To qualify for SMP you must pay tax and national insurance as an employee (or would pay if you earned enough).

Just search on Google for Maternity leave...enough bedtime reading to confuse Einstein !!