The leader of the far-right English Defence League has been jailed for 10 months for using somebody else's passport to enter the United States.
Lennon, 30, pleaded guilty to possession of a false identity document with improper intention, contrary to the Identity Documents Act 2010, at Southwark Crown Court.
Mr Lennon, who had previously been refused entry to the US, used a passport in the name of Andrew McMaster to board a Virgin Atlantic Flight from Heathrow to New York in September.
He was caught when customs officials at JFK airport took his fingerprints and realised he was not Mr McMaster.
Lennon was asked to attend a second interview but left the airport, entering the US illegally.
Mr Lennon stayed one night in the US and then travelled back to the UK the following day using his own legitimate passport - - which bears the name Paul Harris.
Lennon, who was arrested in October, was jailed for 10 months.
The court heard that he was previously jailed for assault in 2005 and also has previous convictions for drugs offences and public order offences.
Sentencing the 30-year-old, Judge Alistair McCreath, told him: "I am going to sentence you under the name of Stephen Lennon although I suspect that is not actually your true name, in the sense that it is not the name that appears on your passport.
"What I have to deal with you for is clear enough.
"You knew perfectly well that you were not welcome in the United States.
"You knew that because you tried before and you had not got in, and you knew the reason for that - because, rightly or wrongly, the US authorities do not welcome people in their country who have convictions of the kind that you have.
"With that full knowledge, you equipped yourself with a passport. I am told that it was given you by way of a loan from your friend Andrew McMaster, to which you bore, I am told, some resemblance.
"And by use of that passport you did what you could to get into the United States.
"But you did not get in because they took your fingerprints and they worked out that you were not who you claimed to be.
"I am told that, by whatever means, you slipped away from the US authorities, got into the country and then very rapidly - and understandably so - got out of it."
He said Lennon had used his own passport to get out of the US, adding: "You did so, I am quite sure, in order to avoid the consequences that would have fallen upon you had you been caught by the authorities in America."
The judge went on: "What you did went absolutely to the heart of the immigration controls that the United States are entitled to have.
"Had it been known in this country that you were proposing to leave under a false passport, you would not have been accepted on to the plane and you would not have been permitted to leave this country on a false passport.
"It's not in any sense trivial."