Herman’s Hermits

Hopwood joined Herman's Hermits in 1962. The Hermits frontman Peter Noone credits Keith with coming up with the idea of recording "Mrs. Brown, You've Got a Lovely Daughter" as an afterthought, when Herman's Hermits were short of material for their first album. Noone's heavily accented delivery, together with Hopwood's muted rhythm guitar work, propelled the track to number one on the US Billboard Hot 100 chart.

During the 1960s, Herman’s Hermits would continue to garner more hits including I'm Henry the VIII, I Am, Silhouettes, Can't You Hear My Heartbeat, and My Sentimental Friend. Hopwood left Herman’s Hermits in 1972.

Producing and composing

Ralph McTell recorded the theme tune to Cosgrove Hall Films's adaptation of The Wind in the Willows written by Hopwood and Malcolm Rowe, and this was released as a single in 1984, after the series was aired on ITV. Hopwood also co-wrote the music for Cosgrove Hall's adaptations of Terry Pratchett's Soul Music and "Wyrd Sisters" with Phil Bush. Soundtrack albums were released in 1997.

Hopwood and Rowe co-wrote and produced the music to the 1989 film adaptation of Roald Dahl's The BFG. Other Cosgrove Hall shows he composed for were Creepy Crawlies, Alias the Jester with Malcolm Rowe, Foxbusters, Andy Pandy, Discworld, with Phil Bush, and Albie, alone.

In 2004, he composed the music for the remake of Pingu for HIT Entertainment, and in 2005, he replaced Paul K. Joyce as composer on Bob the Builder starting with Project: Build it, which was to last until production ceased in 2011.

In 2013, he formed a music rights company, CHF Music, with Cosgrove Hall Fitzpatrick Entertainment, the newly launched company run by Brian Cosgrove and Simon Hall, to look after all the music content for their new shows. In 2017, Hopwood started working on the series "Daisy & Ollie, starring Jason Manford, now produced by Hoopla Animation. There are currently 130 episodes produced.

Pluto Music

In 1968, Keith Hopwood and Derek Leckenby founded Pluto Music, a company that composes musical scores for commercials, films, and animation. Leckenby died in 1994, but Hopwood continues operating the company. Pluto Studios has been very successful, providing services to many top acts including The Clash. Hopwood has proved himself a fine soundtrack composer, working mostly on animated television series including the hugely successful "Bob the Builder." Always a composer, he wrote and co-wrote numerous songs recorded by Herman's Hermits, and other bands such as Brinsley Schwarz. Hopwood also published and promoted the singer-songwriter, Helen Watson. He has also helped create many tracks for his granddaughter, Izzy Hopwood, who has had great musical talent from a young age.

Solo

In 2021 he wrote and produced (along with son Dan) his first solo album Never Too Late. Containing eleven original songs this was released 1 February 2022.