Andrew Rowe was caught trying to travel back to Britain through the Channel Tunnel.
He was found to have a rolled up pair of socks with traces of explosives.
Searches of his former home in London produced notes on using mortar bombs.
And the search of his estranged wife's home in Birmingham had revealed a code "chilling in the extreme" with substitutions for such words as airport and target.
Rowe, of Maida Vale, north west London, was found guilty at the Old Bailey of two offences of having articles for use in terrorism.
But the prosecution decided not to seek a retrial when the jury could not agree a verdict on the socks.
Mr Justice Fulford told British-born Muslim convert Rowe, 34, that he believed he was on the verge of an act of terrorism.
"Whatever your terrorist purpose was, its fulfilment was imminent," he said.
"In the post 9/11 world, it requires no imagination to understand what would have been in your contemplation and what would have been your purpose."
He told Rowe: "You were a paid operative over a substantial period of time, travelling the world and furthering the cause of Muslim fundamentalism. "
Mr Justice Fulford said the maximum sentence for having articles for terrorism was 10 years.
He added: "I want to make it abundantly clear that the Government should give immediate and urgent consideration to the adequacy of that term.
"Ten years is wholly not adequate and the courts should have the option of a discretionary life sentence."
He jailed Rowe for seven-and-a-half years on each charge making a total of 15 years.
He said there would be cases where the circumstances would be graver than that of Rowe, and where the maximum sentence would need to be imposed.Reuse content