Yes, you're correct. The song, "The Sick Note" or "Paddy and the Barrel" was written by Pat Cooksey in 1969, and was based on a speech given by musician and humorist Gerhard Hoffnung at the Oxford Debating Society. Here's a thread started by Pat Cooksey himself, and this is Pat's opening post from that thread:

"Over a long number of years there has been much speculation concerning this song. I wrote this song under it's original title Paddy and the Barrell in 1969, and first performed it in The Dyers Arms in Coventry at this time, and in 1972 Sean Cannon, later to become a member of the Dubliners began to perform it in the folk clubs under the title The Sick Note. The song was based on Gerard Hoffnung's wonderful address to the Oxford Union, but the story in a more simple form dates back to the English music halls in the 1920's and appeared in the Readers Digest in 1937. I personally gave the words of this song to Noel Murphy in a night club in Coventry in the early seventies and his only contribution to this song was to change the title to Murphy and the Bricks, and when this song was recorded Noel Murphy was obliged to remove his name from the writers credits, I still have a letter from Misty River Music to this effect. The song under more than 20 alternative titles has since been recorded more than 100 times worldwide, and in every version the words are identical. This song under all alternative titles has always been the exclusive copywright of myself, Pat Cooksey, and is registered with The Performing Rights Society in London. This includes Dear Boss by The Clancy brothers, The Bricklayers Song by The Corries and Ray Stevens, The Sick Note by The Dubliners, etc,etc, and also Murphy and the Bricks. No other artist had any input into this song nor is any claim for arrangement valid. Pat Cooksey, Nuremberg, Germany."

Aloha,
Mark