The policeman, known as Vincent, infiltrated a group known as the Three Musketeers, who are accused of plotting an attack on British soil
A fellow covert officer told the Old Bailey Vincent, who has denied planting incriminating evidence, was "honest".
The four men deny preparing terrorist acts.
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They were arrested in August, after a partially constructed bomb, a hatchet and imitation gun were found by security services.
Vincent has been cross-examined over his role in the discovery of an explosive device in a car of convicted terrorist Naweed Ali, 29, of Sparkhill in Birmingham.
Ali's Seat Leon had been parked at the Birmingham depot of Hero Couriers, a fake firm operated by undercover officers tasked with infiltrating Ali and his co-accused Khobaib Hussain, 25, also of Sparkhill, through delivery shifts.
Vincent has repeatedly denied the allegation of Ali's defence team that he planted incriminating evidence.
Fellow undercover officer Andy, who was the joint owner of Hero Couriers, was questioned by prosecutor Gareth Patterson QC about allegations levelled at Vincent.
Giving evidence anonymously, Andy said:  "I find that extremely hard to believe. There's nothing to be gained by doing that.
"He has always been absolutely professional in dealings I have had with him."
Mr Patterson said: "Were you under any pressure in the undercover team to find evidence that would allow an arrest to be made that Friday August 26?"
Andy replied: "No, absolutely not."
He also said there was nothing about Vincent's behaviour that looking back seemed suspicious.
Mohibur Rahman, 32, and Tahir Aziz, 38, of Stoke-on-Trent, are on trial along with the two Sparkhill men.
The trial continues.
An undercover officer would have had "nothing to gain" by putting a bomb in a car to frame an alleged terror cell, a colleague has told a court.