Whilst 15,000 tickets were allocated for pitch-standing, seating in the stands had to be significantly reduced to meet health and safety standards.
Liverpool City Council gave £1.7 million to MPL Communications to cover costs such as stage and lighting hire, licence fees and insurance.
manager Rafael Benítez, normally resident in the ground's technical area was in attendance as was a member of his playing staff, Jamie Carragher.
Kay described him as "a local lad who's done very well for himself in the music game" and has "played with some amazing people over the years: Stevie Wonder, Rupert the Bear and The Beatles."
He jokingly thanked the crowd for coming out and "missing the last episode of Ultimate Force with Ross Kemp" and claimed he was dismayed that the previous day's soundcheck had revealed McCartney would neither be breakdancing nor including a Right Said Fred medley in his set.
The encore included the first live performance by a Beatle of A Day in the Life which led into a rousing rendition of The Plastic Ono Band's Give Peace a Chance in front of a giant CND symbol.
Set List Encore McCartney was joined on stage for three songs by former Nirvana drummer and Foo Fighters frontman, Dave Grohl.