Socci - once your child is 3 you cn get the 'early years grant' (I think it is called) - money paid from the LEA to the private nursery, and it subsidises your place by about £25 a week, I think. The nursery will do all the paperwork for you - you just have to fil in a form they give you.
By vouchers, do you mean the tax exemption on your payments to a nursery? That's where you - and DP?DH can both make a salary sacrifice, and money is paid instead in vouchers, or direct from your employer, to a private nursery - and you do not pay tax on that amount.