The TV appeal took place in October 2013. According to JC's book, he claims 'several' callers put forward CB's name. He then mentions one 'key' witness in particular who gave reasons of why he thought CB might be involved. This person was said to be a "former friend" who worked for a swimming pool company near PDL back in 2007.
The summons CB was handed was dated 4th November 2013 and it ordered him to attend the police station on November 6th for questioning in relation to the MM case, where he would be expected to provide an exact account of his "timings and movements" for the entire month of May 2007.
Later in the book HCW confirms to JC that CB did attend the interview, answered their questions and did not seem suspicious at the time. Presumably therefore, CB has already given police an account of where he claims to have been throughout May 2007.
One of them could even be panikspatz... their chat took place in sept 2013, perhaps CB boasted he had indeed done what he was saying he would do - i doubt we have the whole chat. We might have given the whole chat?