Cheeky comedian Lee Mack wasted no time in using the Queen's Platinum Jubilee as an opportunity to stick the knife in Boris Johnson – metaphorically of course.The northern comic, 53, opened the concert, which is being held outside the gates of Buckingham Palace, by making light of the so-called 'partygate' affair in Downing Street. Speaking with the Prime Minister in attendance, who was in the royal box, Mack said: "Finally we can say the words ‘party’ and ‘gate’ and it’s a positive." The joke drew cheers and laughs from the crowd.The embarrassing quip comes just a day after the PM was booed outside St Paul's Cathedral as he attended the Thanksgiving service with members of the Royal Family.