Judge Joyce said that in "panic-driven apprehension'' at the investigation, he made an "entirely amateurish'' attempt to create the fake receipt book.
"It was an exceedingly stupid thing to do,'' he said, particularly as Myles ultimately had nothing to fear about his actions.
Judge Joyce, who heard the case alone without a jury, emphasised that there was no substance to the criminal conspiracy charge against Myles and that he had not merely got the benefit of the doubt.
He said though obstructing justice was a serious charge, Myles could easily have been charged with the lesser offence of producing a document knowing it to be false.
Myles was sentenced to four months community detention and 250 hours community work.
Briggs was jailed for four years 10 months and Clifford for four years for their parts in a swindle of hundreds of thousands of gaming funds relating to a scam involving tennis clubs around Auckland.
Judge Joyce said the tennis clubs were not the main victims of the swindle of gaming machine funds, which must be used for community purposes.
"The `victims' were the charitable organisations that could have benefitted in terms of the objectives of the trust from the vastly greater pool of funding that would have been available but for your wrongdoing.''
SFO chief executive Adam Feeley said it was imperative for those involved with charitable organisations to demonstrate high ethical standards.
"Mr Briggs and Mr Clifford took advantage of their positions and in doing so, deprived the local community of valuable resources.''
Myles was elected as National MP for Roskill in 1990 but left the party to become an independent in 1991, unhappy with National's privatisation plans and its slashing of welfare payments.
He set up the Liberal Party in 1992 with fellow National dissident Hamish MacIntyre but left the following year for New Zealand First when the Liberals joined the Alliance.
Myles lost his seat in the 1993 election. He returned briefly as a New Zealand First List MP in 1999 before that party lost most of its support in that year's election.
- NZPA