Gordon Layton, 56, was found not guilty at an Old Bailey court of conspiracy to defraud Europarks by dishonestly acquiring information about its business affairs.
Simon Hewitt, 38, of Hammersmith, west London, a former manager of a security firm employed to acquire the information was also cleared of conspiracy to defraud.
The court was told that Mr Layton of Regent's Park, London, believed he was acting in a 'perfectly legal and ethical way' when he hired KAS, a security company, to investigate Europarks. He wanted to know how it was winning lucrative car parking contracts and whether there was a leak of information from his own company.
He 'wanted to act in the interests of his company, avoid breaking the law and he wanted to act within what was regarded as ethical', Alex Carlile QC, for Mr Layton, said.
KAS, based in Mayfair, central London, was started by Sir David Stirling founder of the SAS, the court was told.
During the two-month trial, David Paget, for the prosecution, said KAS operatives, may of them former SAS soldiers, followed Europarks directors, searched their dustbins and got jobs as car park attendants.
Jane Turpin, a former Army captain, used a fake CV to get a top secretarial job at Europarks where she photocopied documents and sent regular reports about the company and its personnel to Layton via Hewitt. Charges against Miss Turpin were dropped at the start of the trial after the prosecution was told it would be 'medically inadvisable'.
A preliminary investigation revealed Europarks was winning contracts fairly by undercutting NCP and not by obtaining confidential information about NCP.
Neither Mr Layton nor Mr Hewitt gave evidence, their lawyers arguing that neither believed they were breaking the law.
When Europarks discovered it was were being spied on it sued NCP. A civil action was settled when NCP bought Europarks for pounds 4.3m and paid money to four directors.
National Parking Corporation, which owns NCP, yesterday welcomed Mr Layton's acquittal and called for a review of the law relating to private security services. 'The company remained confident that he was innocent of the charge brought against him. His reputation for integrity is well known.' The trial had been an enormous strain for Mr Layton and his family, but he would be returning to work, it said.
'The fact the trial took place at all has shown the law relating to private security services to be in a very unsatisfactory state and in need of clarification,' it said. Company lawyers were examining 'untrue allegations' made about the case, it added.