Connections to an old British Classic Movie

I am trying to track down an old British relic from the 1950's era. Can't remember the name nor actors but the story line was quite similar to RP. A couple of petty crims, not too bright, kidnapped a dowdy wife of a wealthy man and when they demanded a ransom he told them to keep her. The wife was very upset that her husband took that attitude and unbeknown to her he had a mistress tucked away and when she (the wife) found out the he had been lavishing gifts on the mistress for years, got mad and decided on revenge. She not only joined the crooks but became their leader and set about to fleece her husband. The wife transformed herself and from dowdiness to platinum blonde, fine clothes and furs all put to her husband's accounts (which he used on his mistress). Is there anybody out there who might know of this film?

BlueSkies