We went to the bank yesterday....our interest day was 21st Aug, but the bank doesn't open on Saturday.Anyway after we had completed our transaction, I noticed that the next bank day was to be 27th Sept.I queried this and was told that we had a 35 day account, but the interest would be slightly higher.I told the bank that as we hadn't requested a 35 (actually 37 days) day account to change it back to 31 days.
We worked it out that by having a 35 day account, we would get 10 interest days a year (11 every 3rd year) and the difference in the interest rate was miniscule compared what we would lose on 2 months interest.
By the way this is not the first time the bank has done this.