It wasn't meant to be like this

When David Cameron set up an inquiry into the press - triggered by the revelation that a newspaper had hacked into the phone of a murdered girl - he told the country he wanted to ensure that it could never happen again.

He knew there would be questions not just for the press and the police but for politicians too. What he did not foresee was that the Leveson Inquiry would become, at least in part, a long running trial of his personal and political judgements. Nor did his advisers imagine that this inquiry would force them to trawl not just seven years worth of diaries and official minutes and emails but records and recollections of text messages, party invitations and horse rides.

For hour after hour, day after day, David Cameron's aides have been forced to focus on what he might be asked and what he might say today in Court 73 of the Royal Courts of Justice leading some to mutter that the Leveson Inquiry has transformed into a "monster" which is out of control.

Today after he swears on oath to tell the truth, the whole truth and nothing but the truth Mr Cameron will be asked to explain:

• why, in his own words, he got too close to the media and in particular the Murdochs and their chief lieutenant Rebekah Brooks. And why did he think it appropriate to wine and dine, to party and horse ride with the country's most powerful media executive whose company had an aggressive policy of expansion.

• why he appointed, not once but twice, the man who resigned over phone hacking at the News of the World as his spin doctor - first in opposition and then in government, ignoring all the warnings he was given.

• why he handed responsibility for News Corp's £8billion bid for BSkyB from one minister who'd expressed a clear bias to another who'd done the same.

Many of these answers he has given before. Those which he hasn't have been carefully planned, plotted and rehearsed.

What won't grab the headlines but may, in truth, be the most significant part of today's proceedings is the exchanges between the Judge and the prime minister over what is troubling them both - how to regulate the press. Witness after witness, former prime minister after former prime minister has lined up to say that this moment must not be flunked and this inquiry must not become another lost opportunity. However, Lord Justice Leveson has been reminded again and again of why, again and again, since the war nothing has been done.

Both Tony Blair - who didn't do it and never tried - and John Major - who at least tried but never followed through - told him that the press would fight against any plan to regulate them, the struggle would absorb huge amounts of parliamentary energy and political time and the government would put at risk much of the rest of its agenda.

As David Cameron looks at Lord Justice Leveson and he looks back the biggest question will be the one which is unspoken: "What on earth are we going to do when this inquiry is finally over?"