You're not allowed to carry them in arms so just take your pushchair with you x
We had a car seat that doesn't come off the isofix and they let us take the baby down in the cot they put the baby in and then leave that in reception as someone will take it up to the maternity ward. Or as others said have your pram bought in to take baby down
No one checked my baby in the car seat when we left so maybe you could just put them in their pram and then put them in at the car.. but having a car seat that clips onto your pram is really handy for the first few months so may be worth getting one xx