If you are employed then maternity pay from employer.
If not employed but have worked 26 weeks in the last 66 (thats 66 weeks from due date) then maternity allowance from DWP which is around �112 per week.
If you havent worked the 26 weeks then JSA and, as you get nearer your due date, incapacity benefit (though there isn't much difference between them financially except that you dont have to sign on every two weeks for incap ben). Once you have baby your incap ben will cease after two weeks and you will have to go back on JSA unless you have a doctors sick line.