The flight, which took off from Manchester and was bound for Girona, was diverted to Gatwick when the crew noticed smoke coming from the forward galley.
A Tui investigation later established the galley ovens had been contaminated with a degreasing fluid not designed for use in aircraft.
The plane had undergone a deep clean 48 hours earlier. However, further enquiries found the cleaning company was not responsible for the contamination.
On Thursday (March 8), the Air Accidents Investigation Branch (AAIB) released its findings following the incident on July 8 last year.
Around 15 minutes after take off, cabin crew switched on the forward galley ovens, which began to smoke. The captain was informed and two fire extinguishers deployed to no effect whereby the flight was diverted to Gatwick.
After landing, ground staff assisted passengers from the plane while three members of cabin crew received medical assistance. No passengers were affected.
A Tui spokesperson said the aircraft was found safe to continue its scheduled journey once replacement crew members arrived.
The AAIB report said the ovens in the front and rear galley were all contaminated with a similar substance, later found to be a degreasing fluid used for removing chewing gum from carpets - not an approved oven cleaning fluid.
It also revealed the aircraft was “deep cleaned” 48 hours earlier, although further investigations by Tui and the cleaning contractor established cleaning instructions were clear, referencing the correct fluid, and that the deep clean had been completed using this product.
The AAIB concluded “it was not possible” to identify when and how the ovens were contaminated.
The Tui spokesperson added: “Flight TOM2616 travelling to Girona, Spain from Manchester was diverted to London Gatwick as a precautionary measure.
“The flight was met by emergency services in line with standard procedures and to investigate the cause of smoke in the cabin. The aircraft was checked and found to be safe to continue its scheduled journey.
“All customers on board were safe, and new crew members arrived imminently to cover the flight as three of the original team were checked over by medics as a precaution.
“We would like to reassure everyone that the safety of our customers and crew is of paramount importance.”