Lily Allen caused tension between Harry Potter stars Rupert Grint and Emma Watson - after calling the young actor while he was on a shopping trip with his pretty co-star.

And when Emma, 17, saw it was Lily calling Rupert’s mobile while he was busy trying on a suit in Armani, she slammed the phone down on her.

A fellow shopper said: “Rupert was trying on suits when his mobile rang in his jacket, which he’d hung next to Emma.

“She picked up the call and I heard her say: ‘Why am I answering his phone? Because he’s rather occupied at the moment. Is there something you want?’”

At the time, Rupert, 19, was having his measurements taken by the tailor.

Adds the source: “Emma listened to the person on the phone for a bit and then she said: ‘We’re busy right now, like you should be, Lily.’

“It was then Rupert’s turn to go berserk at Emma for being so rude to Lily and cutting her short. They really had a bicker about it all.”