This is a snippet of this morning’s AM report on the first hearing last night of the inquiry into Australia’s immigration detention network. The angle? A focus on the secretary of the Immigration Department Andrew Metcalfe’s candid comments about mandatory detention:

ANDREW METCALFE: There are a range of policy conundrums. How should we manage the issue of asylum? What is the balance between our international obligations to protect refugees and our need for strong border controls?

NAOMI WOODLEY: And he had some more pointed suggestions on the treatment of asylum seekers who reach Australia.

ANDREW METCALFE: Is immigration detention a deterrent? Does immigration detention facilitate case resolution? What range of facilities should be utilised? For how long is an immigrant arrival and status determination process in a detention centre environment required? There are many questions for you as parliamentarians to consider.

NAOMI WOODLEY: None of the MPs or Senators at the inquiry directly asked Mr Metcalfe to expand on what he meant. Instead the Opposition’s immigration spokesman Scott Morrison was focusing on the sharp increase in the number of serious incidents in detention centres this year.

True to form, really. There is a bipartisanship on this issue, and that is that alternatives to mandatory detention are considered off topic, or unmentionable and certainly not an option.

So let’s speak to both major parties in a language they understand: by focusing on the numbers. Not on arrivals, or serious incidents in detention, although both deserve scrutiny.

Today Bernard Keane focuses on the bottom line. He has crunched the numbers across budget and ANAO documents and calculated that our politicians’ fixation with asylum seekers arriving by boat has cost taxpayers nearly $2.4 billion since 2000. The cost of detaining asylum seekers only — removing costs for deterrence and anti-people smuggling activities — totals just over $2 billion since 2000. During that period, more than 18,000 people have arrived by boat.

Taxpayers have spent about $113,000 simply to detain each asylum seeker, on average, across the period.

As Metcalfe suggested last night, there are many questions for you parliamentarians to consider. So try listening to one of your most senior public servants.