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This month, retired people saw their state pensions rise by just under 5%.

That's comfortably above the current inflation rate.

How come? The triple lock is how come. A formula set 15 years ago

that economists hate, arguing that it's unsustainable and wrong, and that politicians profess to

love and are careful to put in their manifestos. It all sounds a bit mad. So what exactly

is the triple lock? Can we still afford it? And if not,

what's the alternative? Step into the briefing room and together we'll find out.

To discuss this, I'm joined by Carl Emerson, who's a partner at London Economics,

Sophie Hale, who's researched director at the Resolution Foundation, and Steve Webb, who's a partner at London Economics, Sophie Hale, who's research director at the Resolution Foundation,

and Steve Webb, who's a partner at the Pensions Consultancy, LCP,

but over 10 years ago he was an MP,

and indeed he was the pensions minister when the triple lock was introduced.

First of all, let's find out how this formula actually works.

Carl Emerson, if I can pick in with you, can you explain to us exactly what the triple

lock is and how it works?

So the triple lock is the mechanism by which the flat rate part of the UK state pension

system has increased each year.

So the basic state pension, that's available to people who reach the state pension age

before 2016, so they're 75 or over today.

It increases by the triple lock each year.

And the new state pension, which is more generous and available to those who reach the state pension age after 2016.

...