Lily Allen's new workout regime is ''harder'' than childbirth.

The 28-year-old singer has been hitting the weights at Barry's Bootcamp in London and the gruelling regime as left her feeling like she ''might die now''.

Lily - who has two daughters, 19-month-old Ethel, and six-month-old Marnie, with her husband Sam Cooper - posted on Twitter today (24.06.13): ''I did this http://www.barrysbootcamp.com/london-england.html ... this morning, I might die now ... Actually harder than childbirth. (sic)''

Barry's Bootcamp was founded in 1998 by Barry Jay in Los Angeles and the fitness expert now has 10 gyms around the world.

His workout, dubbed the ''the best in the world'' by Barry, is a favourite in Hollywood and celebrity fans include Katie Holmes, Jessica Alba, Jessica Biel and Kim Kardashian.

Lily is making a return to music after 'retiring' to focus on having children and has revealed her comeback album should be ready for release by spring 2014.

She said: ''I'm really enjoying writing it (the album) and hope it will be ready for March. It is very different to what I've done before.''