The Beady Eye frontman squared up to 'The Wire' actor at the Warner's after-party at London's Ivy Club after mocking his bobble hat, and the former Oasis singer also found time to lambast 'Line of Duty' actor Martin Compston's Scottish accent.
An onlooker told The Sun newspaper: ''Liam was in full rock 'n' roll swagger mode.
''He bowled up to the party after midnight and made his presence felt pretty quickly.
''He had a row with a Scottish actor called Martin Compston, mocking his accent.
''Then he had a few words with Idris, poking fun at his bobble hat among other things. Idris looked like he was going to flatten him - they were on completely different wavelengths.''
But fortunately for Liam, Idris - who was with his 'Luther' co-star and former World Thai boxing champion Warren Brown - was ''in a good mood'' and didn't pursue the encounter and the 40-year-old singer left the event soon afterwards.
The onlooker added: ''They were toe-to-toe at one point. Neither of them backed down. Idris was in a good mood, so left it, which was probably for the best. Liam left soon after.''
It's not the first time Liam - who hasn't spoken to his brother Noel since he quit Oasis in 2009 - has been involved in an altercation. In 2002, he had his two front teeth knocked out during a brawl in Munich and had to undergo hours of emergency dental surgery to have tooth implants fitted at a reputed cost of nearly £20,000.
In 1997, Liam was cautioned by police after he leaned out of his car window and grabbed the shirt of a cyclist and pulled him along with the car, while in 2006 he was banned from London's exclusive Groucho Club after squirting a fire extinguisher at former England soccer star Paul Gascoigne.