if i was to use a local vets ooh service, can i just phone up as and when i need it or would i have to be registered there?

The first time i had a litter i was caught out in the middle of the night with my bitch who had to have a c section at vets now and we ended up with a vets bill for 1700 pounds.it was straight forward too. they actually quoted me 1000 but with all the meds etc and gas they said it went up to 1700 i couldnt believe it but the have ya, so it nedded to be paid. after that i found myself a vet who did his own out of hours and atleast then they know the animal that they are dealing with too , it puts my mind at rest.

When my vet closes at 630, they transfer over to a night vet in a different surgery...this  vet charges £110 just to be seen and before any treatment.
Thankfully we havent had to use this one, but my friend who has quite a poorly dog has on several occasions...with trips to her usual vet and then the night time ones its cost her a fortune.