since the days of Tony Blair and New Labour.

So, what is it and why does it matter?

Here are the three things you need to know.

First, it means Britain's lowest-paid workers will receive big pay rises⏤not just this year, but every year between now and 2020.

The national living wage is really just a new minimum wage rate that applies to everyone aged 25 and over.

But, it'll be higher than the current minimum wage and it will go up more quickly.

The government plans to start at £7.20 an hour on April 1, then push it up faster than average pay so that by 2020, it will be worth 60% of median earnings.

That's about £9 an hour.

By that point, a lot more people will find themselves on the minimum wage.

Between 2015 and 2020, the number of workers aged 25 and over who are on the minimum wage will treble from 1 million to 3.3 million.

The second thing you need to know is that Britain is not alone.

Countries all over the world are either introducing minimum wages or pushing them up, in an attempt to do something about stagnating living standards.

Germany introduced its first-ever minimum wage last year.

Meanwhile, some US cities like Seattle are increasing their minimums to $15 an hour.

So, how does Britain compare?

At the minute, our minimum wage is in the middle of the pack.

It's not the lowest by any means, but it's nowhere near as high as places like France and Australia.

The national living wage will change that picture.

By 2020, the UK will have one of the highest minimum wages in the developed world.

The third thing to know is that no one is entirely sure how this national living wage will actually work out.

It all depends on how employers react to the fact they have to pay people more.

They could just accept that they're going to make less profit, or they could put up their prices.

Alternatively, they could give workers more training and time-saving technology so that they're more productive.

That would make the higher pay more affordable.

The worst thing would be if they just make do with fewer workers because they can't afford to keep employing all of them.

That could lead to higher unemployment.

So far, Britain's experience with the minimum wage, which is first introduced in 1998, has been good.

It's increased pay a lot for people at the bottom of the ladder without causing any job losses.

But both optimists and pessimists agree that the national living wage is a step into the unknown.

Sarah O'Connor, "The Financial Times", London.