To get it back I would recommend claiming April and then you'll be lucky to get it back by August. Chase it up frequently, it's a right royal pain in the a**e.
Remember that you can hold all PAYE payments back throughout the year. These are off-set againt your CIS kitty. Tell HMRC though, don't just do it.
Unfortunately VAT is a different kettle of fish and has to be paid regardless of how much CIS has been deducted.
I like to think of it as an interest free loan our lovely Government each and every year :
