In an almost Zelig-like career, the Belfast-born troubadour has jammed with the Led Zeppelin legend Robert Plant at ‘Whispering’ Bob Harris’s birthday party (the veteran DJ Harris regards Houston as ‘one of Britain’s great songwriters’) and Houston opened for the likes of Van Morrison and Elvis Costello. But in 2009 Brian Houston topped the lot, when he had breakfast with none other than US President Barack Obama – well, kind of…