I haven’t read anything by Barrett and am probably not inclined to.
I think it is clear that Jesus uses the phrase in its full Biblical sense; I think it’s a waste of time to argue otherwise.
I don’t seek out Muslim attacks on Jesus and scripture because I don’t think that many devout Christians would be affected by that. Counter-arguments from Islam and Judaism, for example, are to be expected, in their deference to their own system of beliefs. Such remarks are just baiting people to argue. Perhaps this does has a place in a forum on apologetics, but you have to be more specific.
Have you done an internet search on Barrett, perhaps? Is there something particular you want to discuss?
Here it is in the NABRE which is a very good translation.
“Jesus, knowing everything that was going to happen to him, went out and said to them, “Whom are you looking for?” They answered him, “Jesus the Nazorean.” He said to them, “I AM.” Judas his betrayer was also with them. When he said to them, “I AM,” they turned away and fell to the ground.”
Note what the guards do when Jesus speaks the Divine Name. Remember in Jewish thought and teaching a name is not just an identifier, it is the very essence and power of the thing. That’s why the Divine Name could not be spoken by anyone except the high priest and then only once a year when he entered the holy of holies. Even in synagogue when passages in the Old Testament came up that included the Name it would be replaced with “the Lord” or “Adonai.” So in this verse from John when Jesus speaks the Divine Name the guards are so shocked and horrified that they fall on their faces. That makes no sense at all unless Jesus had spoken the Name of God.
I googled his name and there seems to be some contradictory beliefs attributed to him. I can’t find any expanded quotes from him, just the same one liners over and over. If he did believe that he is in a tiny minority of biblical scholars. One of the websites that attributed the belief to Barrett that Jesus wasn’t naming Himself as God in John said that part of the reason for the belief is that Jesus doesn’t do that in any of the other Gospels. Of course that’s not true as Jesus uses the Name in Mark.
And simply being a scholar doesn’t necessarily mean much. Remember a while back when this group of scholars supposedly found the Jesus family tomb?
The defense is in the Holy Writ (scriptures) which have been canonized by the Church.
Muslims cannot defend Islam except in that same way.
The difference is in the historical background of the Bible. Whatever else you say about it, events like the Exodus and the Crucifixion are taken to be historical events with a rich theological insight.
It is far-fetched, about as far as fetched can be, that a Muslim is going to correct a Catholic on the meaning of scripture. Heretics have historically argued from scripture, so, ultimately it is the magisterial tradition of the Catholic Church that ensures the correct understanding of scripture.
I don’t recall where to find the evidence in the Koran, but it is based not on orthodox Catholic teaching, but on the Arian heresy, which was widespread during the age of the Prophet Mohammed. So, the words “I AM” won’t make any sense to a Muslim, in the first place, because they don’t believe that Jesus is divine. So then, why would those words make sense to them. And, why waste much of our time here on a point of discussion without the evidence that would in any way support the Muslim thesis or demonstrate the misunderstanding of Christian faith? (I suppose that’s the reason – just take a pot shot and see what you hit.)
Why are you asking US what Barrett said? Didn’t the Muslim person offer his/'her evidence? Isn’t this discussion d.o.a. without a specific and authentic starting point?
Being a scholar by no means qualifies anyone as a theologian. A scholar is someone who is really good in a classroom and following the latest trends of acedemia in their field. What a Christian needs to look for is not how many degrees they have but rather what their philosophical position is on what you believe in in the non-negotiable matters. Someone’s philosophy is much more important than IQ.
Paul also used the same phrase of himself when he said that he wished all men were as “I am” (Acts 26:29). Thus, we conclude that saying “I am” did not make Paul, the man born blind or Christ into God. C. K. Barrett writes:
Ego eimi “I am”] does not identify Jesus with God, but it does draw attention to him in the strongest possible terms. “I am the one—the one you must look at, and listen to, if you would know God.” 
C. K. Barrett, The Gospel According to St John (Westminster Press, London, 1978), p. 342
By the way, I found the quotation on a unitarian website. It is funny how they argue every time someone says I am he should be God for trinitarians
But that’s not what Jesus says. Simply saying for example I am a poster on Catholic Answers is not the same as Jesus answering “Before Abraham was, I am.” Just think about the context of the verses. Why did the Jews pick up stones to stone Jesus after He made that statement unless they perceived it to be a blasphemy? Why did the soldiers fall on their faces when Jesus answered “I am”? Why did the high priest tear his garment when Jesus answered “I am”? The high priest himself calls that answer blasphemy. Whatever Mr Barrett thinks it seems plainly obvious to me what the Jews at the time thought. There is nothing else to explain the reaction.
That is the question, and others, that I would have asked Barrett. I don’t have a problem if a Muslim uses this. The issue is the idea of Jesus using I AM not meaning God is there. But I wouls say please, the Jews explain why they want to stone him!
So, anyone who could add anything?
By the way, Barrett was a Reverend (which confuses me some more about his views)
Charles Kingsley Barrett FBA (May 4, 1917 – August 26, 2011) was a British biblical scholar. He served as Professor of Divinity at the University of Durham, and wrote commentaries on Acts, John, Romans, 1 Corinthians and 2 Corinthians.
Barrett has been described as standing alongside C. H. Dodd as “the greatest British New Testament scholar of the 20th century.”
Morgan, Robert (5 October 2011). “The Rev CK Barrett obituary”. The Guardian. Retrieved 30 September 2013