This souvenir letter card of mine is a fore-runner of the Good Luck one and it dates from 1938. A concertina of 6 photo views of (named town) was attached to the inside and the back of those views could be written on if required at Letter Rate cost of 1½d. Otherwise the card could be sent unsealed and unwritten for a halfpenny.
The 1950 Southampton card is obviously Scottish in manufacture with the tartan bow, the white heather and the Scottie dog... just the named town/city changes to suit the locations.