Unless the full transcript of the interview becomes available, then you cannot say with absolute certainly, what was "outrageous"
From a 2009 article at The Guardian:
"As well as pursuing a new appeal in Scotland, Mitchell's defence team has lodged a complaint with the European Court of Human Rights (ECHR) about his pre-arrest interview, which, in accordance with Scottish law, was conducted without a solicitor present. Despite denying last year's appeal, the three judges said some of the police questioning of Mitchell was 'outrageous'."
I put the word "outrageous" in quotes because it was, in fact, a quotation. My own view is that the very notion allowing a 15-year-old to be questioned without a solicitor is shocking failure of the criminal justice system of Scotland, before one even gets to the mind boggling way in which the questioning was done. From the Daily Record:
"He [Lord Hamilton] added: At times the nature of the questioning was such that the questioner did not seem to be seriously interested in a response but rather endeavoring to break him down into giving some hoped-for confession by hostile interrogation."