Ed Sheeran’s hit Shape Of You was created “from scratch” at “extraordinary speed”, producer Steve Mac has claimed in the High Court dispute over the song’s copyright.

The record maker – whose real name is Steven McCutcheon – joked that he was left with “a headache”, such was the intensity of the session in which the song was written in October 2016.

Mr McCutcheon, Sheeran and third Shape Of You co-author John McDaid are locked in a legal battle with two songwriters, Sami Chokri and Ross O’Donoghue, who claim the 2017 song rips off parts of their 2015 track Oh Why – something they all deny.

Mr Chokri, a grime artist who performs under the name Sami Switch, and Mr O’Donoghue claim that an “Oh I” hook in Shape Of You is “strikingly similar” to an “Oh Why” refrain in their own composition.

They reject a claim that Shape Of You was created from scratch over about two hours at Mr McCutcheon’s west London Rokstone Studios, arguing that it was unlikely Sheeran arrived without “preconceived ideas”.

Taking to the witness box at the High Court in London on Thursday, Mr McCutcheon echoed earlier evidence from Sheeran and Mr McDaid by saying the case was “not about money” but “to clear my name”.

He told the court that working with Sheeran on Shape Of You was an “extraordinary experience”.

“I had a headache at the end of the day,” he said, adding: “It was the first time I had written with anyone like this. It was incredible.”

Andrew Sutcliffe QC, representing Mr Chokri and Mr O’Donoghue, suggested one explanation for the recording session on October 12 2016 was that Sheeran was “unlike any musician you ever worked with”.

But he alternatively suggested it was because the singer had “already worked out how he wanted this song to sound” and “already had lyrics and ideas which he was able to deploy at speed”.

Mr McCutcheon said he disagreed, adding of Sheeran: “The speed that he writes is extraordinary to the point that we can write 26 songs in a week”.

In his written witness statement, the producer, who has worked with artists including Boyzone, Westlife, JLS, Clean Bandit, Pink and Bastille, said creating Shape Of You was a “rapid process”.

He said he had a “clear recollection that Ed, Johnny and I created Shape of You from scratch at Rokstone Studios on the day of our first meeting”.

Mr McCutcheon told Thursday’s hearing he initially supplied the marimba sound on the track and was also “chipping in with lyrics and melody on the day”.

He disagreed with a suggestion that Sheeran led the session, later adding: “He was coming up with the whole song with Johnny and myself at extraordinary speed.”

In his written statement, the producer described the singer “spontaneously singing a stream of melodic and lyrical ideas” and being “a whirlwind of ideas”.

“It was such a quick process, it was hard to keep up,” he said, adding: “None of the melodic, musical or lyrical elements existed before we started work in the studio together.”

He said he had not heard the song Oh Why before the litigation and had no reason to believe any element of it was copied in Shape Of You.

Sheeran had claimed it was Mr McCutcheon who suggested changing an initial “Heya” phrase to “Oh I” on the track.

But the producer told the court he did not originate the “Oh I” phrase and could not remember who did.

In his written witness statement, Mr McCutcheon, who said he has had around 190 worldwide hit singles during his career, noted that clearance was previously sought over a similarity between Strip That Down – a song penned by him and Sheeran – and It Wasn’t Me by the artist Shaggy.

The court has previously heard clearance was sought over a subsequently changed reference to TLC song No Scrubs on Shape Of You.

Mr McCutcheon said in his written statement he “strongly” disagreed with an apparent suggestion that the two occasions showed he had “a habit of plagiarising other writers”.

He wrote: “I always strive to create totally original songs unless I feel, in a particular case, that it would enhance a song to use a reference to another work.

“If I do so, I give credit where credit is due and inform my publisher so that clearance can be arranged.

“There is nothing wrong with referencing other songs in that way if clearance is obtained.

“I am an internationally successful writer of many years’ standing – it would be totally unacceptable to me to go around copying the work of others in the manner suggested, and I would not have achieved the success I have if I did so.”

Legal proceedings were launched by Sheeran and his co-writers in May 2018, with them asking the High Court to declare they had not infringed Mr Chokri and Mr O’Donoghue’s copyright.

In July 2018, Mr Chokri and Mr O’Donoghue issued their own claim for “copyright infringement, damages and an account of profits in relation to the alleged infringement”.

Mr McCutcheon’s live evidence concluded on Thursday, with the trial before Mr Justice Zacaroli continuing.