Clifford Stanford, the founder of Demon Internet and Redbus, pleaded guilty on Thursday morning to unlawful email interception.
Codefendant George Liddell, a former employee of Redbus, also pleaded guilty to the same charge. Both men were sentenced to six months imprisonment, suspended for two years. Stanford was also fined £20,000 and ordered to pay £7,000 towards prosecution costs. The trial had been expected to run for up to two weeks.
Stanford and Liddell were charged under the Regulation of Investigatory Powers Act 2000 with intercepting emails belonging to John Porter, son of Dame Shirley Porter and former chairman of Redbus.
This is the first time that anyone has been prosecuted under RIPA, according to the defence council.
Dame Porter was a key player in the "homes for votes" scandal of the 1980s, under which council homes in Westminster were sold to potential Conservative party voters. She was hit by a surcharge of £37m after an inquiry into the affair, but insisted that her assets only totalled a few hundred thousand pounds.
It emerged during the trial that Liddell was a private investigator, hired by Stanford to gather information about John Porter after the two men fell out. Stanford, who resigned from Redbus in 2002, had hoped to win control of the company by forcing Porter to resign from the board.
The court also heard that a mirror rule had been set up on the Redbus server which sent a copy of all Porter's emails to a Hotmail account set up by Liddell. According to those familiar with the case, the intercepted emails included details of Dame Porter's financial situation.