Mr Sanders is said to have gone for the former Lib Dem press chief's throat in Monday's incident, which hit national headlines at the party's annual conference in Bournemouth.
A Lib Dem spokesman told the Herald Express that Mr Sanders 'pushed' Mr Littlewood, who then fell over a small wall.
The incident was widely reported as 'a kerfuffle'.
Lib Dem officials also issued a brief statement, confirming Mr Sanders had offered a full apology to Mr Littlewood.
But, citing an agreement with his party and Mr Littlewood, the Bay MP has steadfastly refused to either expand on that statement or explain the full detail of what happened or what prompted his actions.
But the Herald Express has now spoken to two eye-witnesses, who claim the incident was more serious than originally reported.
Bristol-based Lib Dem councillor Steve Comer and party member Julian Harris have both published internet blogs revealing what they say is the full extent of 49-year-old Mr Sanders 'unacceptable' assault on Mr Littlewood, which happened outside the party conference venue in Bournemouth on Monday morning.
Cllr Comer, who represents the Eastville ward on Bristol City Council, said he was 'horrified' by Mr Sanders' attack.
He said: "Clearly, for whatever reason, the red mist descended. I was pretty horrified at the time."
In his account on the Lib Dem Voice website, Cllr Comer wrote: "I was handing out leaflets for a lunchtime fringe meeting I was chairing for my trade union when Adrian Sanders pushed past me, almost knocking me over.
"He grabbed Mark Littlewood by the throat, and shook him, Mark then fell backwards over a low wall. Following the attack, I stood between Adrian and Mark to prevent a repetition.
"Stewards and Bournemouth Centre security staff then intervened, and I understand the incident was recorded on CCTV.
"To dismiss this as a 'kerfuffle' is inaccurate. I see that a written apology has been accepted, so that should suffice, and if it was a case of 'red mist' then that has probably been admitted. However this sort of behaviour is unacceptable and as Liberal Democrats we should say so."
Mr Harris published his version of events under a headline which read: 'Exclusive: Eye-Witness Account of Adrian Sanders' Violence'
He wrote: "Yesterday morning Adrian Sanders, Lib Dem MP for Torbay, violently assaulted someone outside the Bournemouth International Centre."
He continued: "Mark Littlewood, ex-PR guru of Cowley Street, was lingering outside the centre.
"Adrian Sanders approached, confronted him, then after only several moments of conversation suddenly attacked him, trying to grab his throat and pushing him backwards over the low wall that he had been standing in front of."
He continued on his online blog: "How can the party claim it is 'not a huge deal' when one of their MPs physically attacks someone at conference?
"There were several other witnesses to the assault, mainly people from Liberal Democrat groups or charities handing out fliers, and the consensus among us was that this is shocking and unacceptable.
"At an event which is supposed to be promoting reasoned discussion and debate within the Liberal Democrats, I find it strange that an MP is essentially allowed to get away with physical assault."
When these versions of events appearing on-line were put to Mr Sanders at his Paignton home yesterday, he said: "There are several versions of the story out there, including one that I punched him, so if I deny or confirm something, then I am commenting on the incident, and I can't do that."
When Mr Sanders was asked if he owed his constituents an explanation for the incident, he said: "What they know is that I don't break my agreements, that is what they will take from this.
"I am not going to comment, my constituents now know that I don't break my word."
When asked if he was accountable to his constituents, whose votes elected him into office first in 1997, then again in 2001 and most recently in 2005, Mr Sanders said: "No more. I have said all I am going to say. Stop. I'm going to put the phone down."
Following Monday's events, Mr Sanders met with party whips who decided he could keep his position as deputy chief whip.
The Liberal Democrats yesterday refused to answer further questions put to them by the Herald Express.
We asked if the agreement that Mr Littlewood, Mr Sanders and the party had reached was in accordance with party disciplinary procedure, and asked the partyto respond to the eye-witness accounts.
But Lena Pietsch, head of media for the Lib Dems, would not comment further on the incident, or the allegations made by witnesses saying: "The party only made one official statement relating to this matter. It was issued on Monday, September 15."
That statement read: "Following an incident this morning, Adrian Sanders MP has offered Mark Littlewood a full, written and unreserved apology for his conduct. On this basis Mark Littlewood will not be involving the legal authorities. Mark Littlewood, Adrian Sanders and the party do not intend to comment any further."
A spokesman for the Bournemouth International Centre, where the incident took place said there was no CCTV footage of the incident.
Mr Littlewood said he would not comment further, saying: "I stick by the statement that I agreed with the press office."