Comey does not have clearance now.
"Benjamin Wittes, Senior Fellow at Brookings tweeted that during a text message exchange with Comey, he asked the former FBI director if there was even anything for the White House to revoke. Comey reportedly responded "nope," adding that he was "read out" when he left government and later declined a temporary clearance to read a classified version of the DOJ'S inspector general report."
Also, if called to testify, all he needs to do is read a part of his book aloud as the process for every step of the investigation of Clinton's email is there along with the reason he made every division in that case. He made no decision by himself, every one was after the investigative team discussed the matter of what should be done, even down to the wording he would use when making a statement to the public.
I am posting available information which doesn't mean I "love" Comey - I have no "feeling" one way or another about the matter.