it was said in the sit com with Denis Waterman and Joan Simms(Stay lucky?) who plyed the part of Mrs Wembley, the phrase was said by the chauffeur who was the husband in Barbara but cant recall his name. A bit vague but hope it helps
fourteen85
Sam Kelly is the actor who played the chauffeur.
I seem to remember it being Mrs. Webley (Joan Sims) who said "Just the one", in reference to drink.
Yes it was Joan Simms who said 'just the one' but as time went on and she was asked if she wanted a drink then before she could reply the chaffuer would say'just the one Mrs Wembley?'