Pop star Lily Allen uses a secret pen name when writing songs for other artists.

The Smile singer has revealed she works on tracks which are recorded by other stars, but she keeps her true identity hidden by using a pseudonym for all her extra songwriting.

She tells Popjustice.com, "Well! I may have a pseudonym. I may have a writing name, and I may have written other songs!"

When pressed on whether she has actually done so, she adds, "Yes" but refuses to name the artists she has given her songs to, adding, "I'm not going to tell you... One day you'll find out..."