Thanks everyone, I spoke to our accountant today and he spoke to HMRC, it would appear that I cant delay the start of SMP until after the baby is born, it kicks in the day after Pickle arrives. I guess I understand why.
But interestingly HMRC said that if are still owed holiday for that year that you havent taken, you shouldnt have to loose it but that your employer can pay you SMP and holiday entitlement in the same week. So I with regard to my holiday entitlement, I dont have to 'use it or loose it' - which is great and what I was worried about.
The alternatives are tack it on the front (but that means less money in my pocket) or at the end (but some employers dont like carrying holdiay over).
Thanks everyone for taking the time to respond.
xx