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We had one but it was in church and tbh it lasted about 5 mins. You stand here, you stand there etc. mind you I got terrible giggles when rehearsing vows which freaked me out for doing it for real. If your comfortable not having one and trust the registar to direct you all on the day then don't bother.
I know churches offer one, but does there need to be one for a civil ceremony?
The registrar charges about £100 extra for the rehearsal. The wedding is in an approved premises, but one which does not have a dedicated wedding co-ordinator (ie a hotel or something). The woman in charge of the premises is there and I'm sure can give us a fair idea of who stands where and what needs to be done.