I mentioned Fry's Five Boys Chocolate, as it was known, but was met with a blank. Not surprising as it was withdrawin in 1972, several years before this person was born.
As I remember, the bar had a soft centre with each section a different flavour.
It was pure serendipity that someone on The Antique Roadshow brought along a collection of chocolate bars which had been rescued from ancient station vending machines having fallen down inside, and one happened to be a Fry's Five Boys. The image is a screen-grab.