Tesland

Tidman was an MI5 agent.

In 1965, he and fellow agent Jimmy Bondson were to rendezvous with Captain Blacker, who had collected the plans for a nuclear device with the potential to endanger the entire world, on his yacht off the coast of Monte Carlo, so that Blacker could hand them over to him and Bondson while maintaining cover. However, as Tidman and Bondson approached in a boat which Tidman was driving, they witnessed the explosion of Blacker's yacht. Tidman wondered if the reason for the explosion was the fuel tanks, reasoning that the craft was petrol driven.

Believing that Blacker could be trapped at the bottom of the ocean as well as noting the urgency to obtain the plans, Bondson donned diving equipment to investigate the wreckage. Before he left, Tidman warned him to be quick in case the police arrived but Bondson instead told him to communicate with the authorities via the radio and to "explain things [...] just enough to keep them happy". When Bondson reached the yacht, Tidman asked him how bad the damage was and when he discovered Blacker's corpse, he concluded that nobody could have survived such an explosion.

Bondson then revealed that Blacker had not died in the explosion but had been shot five times and with a gun of unusual calibre. Tidman thought the cartridge cases could have given them a lead to the murderer but Bondson shut him down, telling him that it was not their problem and that their job was finished as soon as they located the plans to the device. He made a final radio call, telling Tidman they were too late and that the plans had gone, the explosion having been no accident.

Bondson later called International Rescue for help in locating the plans and they were ultimately successful in detaining Carl and his gang. Lady Penelope returned the plans to Bondson, who came alone, in the Forest of Digne. (TV: The Man from MI.5)

Other sources dated the activities of International Rescue to the 1990s, (PROSE: The Dying Days) the 2060s, (PROSE: Titan Declares War! et al.) and the 2080s. (PROSE: Captain Scarlet in Death Crash! et al.)

Behind the scenes
The puppet which "played" Tidman was also seen in several other episodes of Thunderbirds. It had more speaking roles as Collins in Danger at Ocean Deep where he was again voiced by David Graham and as Percy's friend in The Duchess Assignment where he was voiced by Ray Barrett. The puppet appeared in a silent capacity as a security guard in Move – And You're Dead and as a hotel guest in The Cham-Cham.