Phoebe Waller-Bridge’s sister Isobel has released her latest single, called September, on post-classical record label Mercury KX.

The 35-year-old, best known for writing the music for Fleabag, recorded the track for the compilation album Flow, which celebrates the label’s third anniversary.

Waller-Bridge, whose recent credits include Emma, Black Mirror and Vanity Fair, signed to the label ahead of the release of her second album.

She is working on the untitled record in her recording studio in Hackney, east London.

Waller-Bridge said: “September is my hello to the label. I’m so excited to have signed with Mercury KX and also to start work on what will be the most personal music of my career.

“This has been my dream since my teens. I still can’t quite believe it’s happening.

“September came out of an improvisation. It won’t be on my album, but it’s a signpost. It has a clarity and intimacy that reflect the very personal journey I am about to go on.

Phoebe Waller-Bridge comments
Phoebe Waller-Bridge (Matt Crossick/PA)

“My approach is always simplicity. I feel really present at the moment and I want the music to capture that.

“Building my own studio was the ideal start. I have a baby grand piano which has been in storage for eight years. Finally getting it back in situ feels really important to this project.”

Waller-Bridge shot to fame after scoring the Golden Globe-winning comedy-drama series Fleabag, which was written by and starred her sister.

More recently she was invited to score the late Alexander McQueen’s spring/summer 2020 collection for Paris Fashion Week.

The British Fashion Awards 2004
Alexander McQueen (Yui Mok/PA)

She said: “I’m starting from scratch, which is really refreshing.

“It makes me feel free because it means I can go wherever I like. I loathe to use the word unique, but this project will be set far apart from my other work. All of this album will come from within.

“As yet, there is no specific concept, but I do know that I want to create a whole world. Perhaps collaborate with a cinematographer to take the listener on a journey.

“I like the idea of entering an album being like going through a door and, by the end of it, you can see the mountain.”

Mercury KX was launched by Universal Music Group and Decca Records as a platform for experimental post-classical music.