Taken from the 1983 movie The Dresser, with Albert Finney, as the veteran actor Sir speaking these lines.

The movie tells the story of a touring Shakespearean theater group in the 1940's. a backstage hand - Norman, the dresser, played by Tom Courtenay - is devoted to the brilliant but tyrannical head of the company. He struggles to support the deteriorating star as the company struggles to carry on during the London blitz.

The pathos of his backstage efforts rival the pathos in the story of shakespeare's 'Lear' and the Fool that is being presented on-stage, as the situation comes to a crisis.

The line is quoted in p.c.p. as a reference to shakespeare being regarded not politically correct by some during the 80's and 90's. 'Sir' not remembering the original lines can therefore symbolize pc changing lines in plays or works of art to make them politically correct, thus rendering the old versions impotent. (Thanks to Graham for providing this interpretation).