The first release was in February 1968 by the Bystanders, whose manager Ronnie Scott co-wrote the song with Marty Wilde, using the pseudonyms Jack Gellar and Frere Manston. At that point it was called When Jesamine Goes. As far as I can tell it did not make the charts.
The Casuals released it in May the same year, and took it to No 2 in Britain. I don’t think it was released in America.
Here is a mimed performance but the sound quality is dire.
That’s one of the great 60s singles. The version by The Bystanders (who became Man) isn’t very good.
I don’t think the Casuals did much else. They had a minor hit called “Toy” which was OK. Here’s a groovy 1960s clip of it:
https://www.youtube.com/watch?v=5oqyjV5Gbec