Putting the "party" back into the Labour party conference, Mr Brennan, the children's minister, took to the stage with his House of Commons rock band, MP4.
Along with his fellow Labour MP Ian Cawsey on bass, Conservative Greg Knight on drums and Scottish Nationalist Pete Wishart on keyboards, the cross-party quartet packed out their "Never Mind the Politics" gig in the main conference hotel.
Mr Brennan, who plays lead guitar and sings, also pens songs for the band. But the biggest crowd-pleasers in the set proved to be cover versions of songs by The Beatles and Oasis.
"They were all very lively and got everyone going," said one new fan who attended the performance. "They sounded quite professional."
That news will come as something of a relief to Mr Wishart, who played full time with the band Big Country and the folk-rockers Runrig before entering Parliament. He holds the distinction of being the only MP to have appeared on Top of the Pops.
Mr Brennan assured The TES that the proceeds from the conference show would be going to charity, and not towards his party's election war chest.