Ella Purnell has admitted she has struggled with ''anxiety and depression'' since she was a teenager.

The 21-year-old actress revealed that a ''bad experience'' during her school years when she was 15 left her in a poor state with her mental health, and resulted in her self-harming.

She said: ''I have anxiety and have had depression in the past. When I was 15 or 16 I had a bad experience at school - some issues with other classmates and somebody I was seeing, we don't need to go into it.

''I started self-harming and did that for a long time until my mum caught me and I started to learn about it [mental health]. I thought depression was something you could only have if your parents died, or you were really ill and about to jump off the bridge.''

The 'Miss Peregrine's Home for Peculiar Children' actress insists she never had the confidence to speak out about her struggles at the time, but now understands the importance of seeking help.

She added: ''I certainly didn't feel comfortable enough to talk about it then. Had this happened to me now I'd feel able to say, 'Mum, I need to take some time off school', or, 'Mum, I am suffering with this thing'.''

Now, Ella has a host of A-list celebrity friends to call upon when she needs someone to talk to, and has dubbed fellow actress Keira Knightley as one of her ''mentors''.

Speaking to the latest issue of ES magazine, the 'Churchill' star said: ''Keira Knightley remains one of my mentors. I absolutely love her and will turn to her for industry advice or reassurance or validation at any time. She is very classy and elegant and lovely. I have a bit of a woman-crush on Keira.''

The full interview with Ella appears in the new issue of ES magazine, which hits news stands on Thursday (12.04.18).