Lily James worries she wasn't ''focused'' enough while filming 'Mamma Mia! Here We Go Again'.

The 29-year-old actress had a ''really special time'' shooting the musical sequel with the likes of Meryl Streep, Colin Firth and Cher but she's concerned she had too much fun at the expense of her work.

She said: ''Without being too overly sentimental, it was a really special time.

''I worry now that I potentially should have focused more and stopped having fun. We just had such a good time that I forgot to... worry.

''It was just mad, with all these total legends walking around.''

Despite her own success, Lily admitted it was intimidating being around such huge stars.

She said: ''It's intimidating because these are people you've looked up to, idolised, you never expect your paths will cross.''

A highlight for the British star was recording her vocals for the soundtrack with Abba's Benny Andersson and Bjorn Ulvaeus.

She told Britain's Marie Claire magazine: ''I was literally at Benny's recording studio in Stockholm. Out of London, it felt like we existed in this little ulterior universe, just me and the boys from Abba.''

However, the former 'Downton Abbey' actress has no plans to embark on a pop career, particularly as she has damaged her voice over the years due to ''stress''.

She said: ''In no way did it make me feel like [a pop career] was my calling.

''It did make me realise I love singing... I used to sing all the time.

''I think acting sort of took over and I also screwed my voice. I kept losing it from stress. It started in Cinderella.

''You can't miss a day, so you keep talking through it and go on steroids - and over the next few years I damaged it so much, I stopped singing.

''I got into a weird relationship with my voice where I was frightened of it, but the tone changes as you age. It was freeing and wonderful to embrace it [again].''