Many thanks for your helpful replies. Food for thought.

Being a pensioner[to prevent £6 charge I usually leave enough money in account to cover the interest charges. This time I knew my pension was due on 19th which unfortunately clashed with an outgoing leaving not enough to cover the interest charges. Fool me thought [what cat did] that the incoming pension would cover it - no such luck. Seems the computer processes all outgoings, apply charges then processes incomings on same day. I think this is criminal.