Funny Money by Ray Cooney

Jean is preparing a birthday dinner for her mild-mannered accountant husband Henry. Good friends Betty and Vic are expected any minute, and Jean is frantic because Henry is late. When he eventually arrives, Jean finds him not quite the man he used to be. He wants to emigrate to Barcelona immediately, and with good reason: the briefcase he accidentally picked up on the Underground is stuffed with bundles of fifty pound notes amounting to £735,000! But if getting the money was easy, keeping it proves harder, as not one but two police inspectors call and Henry, Vic, Betty and a bemused (and tipsy) Jean are forced into a frantic game of cat and mouse.