THIS week saw a significant milestone in Scottish politics.

In the blazing sunshine in Edinburgh, the three leaders of Scotland's pro-UK parties - me, Johann Lamont and Willie Rennie - came together to make a joint promise.

We all want an increase in powers for the Scottish Parliament and we are all guaranteeing that this will be delivered in the event of a No vote in September's referendum.

I know that many people in Scotland are rightly nervous of the huge uncertainty separation from the UK would bring. We have no real idea what our future relationship with Europe would look like, how we would ensure the defence of an independent Scotland, or even what currency we would use.

But I also know that many of these same people believe in a strong Scottish Parliament.

We want to ensure a positive outcome in the referendum for these people: a Scottish Parliament which has more powers which still retains the security of the United Kingdom.

Some of those powers have already been agreed by all the parties, and were voted through in the Scotland Act 2012.

They will come on stream within months of a No vote this September. But the pledge by us, Labour and the Liberal Democrats on Monday is to go further.

The powers of the parliament should be increased, particularly in the areas financial responsibility and social security.

I believe the Scottish Parliament should have full income tax powers and responsibility for welfare issues which relate to devolved areas, such as housing benefits and attendance allowance.

So if a Conservative government is elected at the next Westminster elections, we will get to work to devolve these powers to the Scottish Parliament.

However, the key element of our joint pledge is that whatever government is in power at Westminster, Holyrood will receive greater powers after the next United Kingdom general election.

The key point is that we can have the best of both worlds.

I believe that the pooling and sharing of resources across the United Kingdom is to Scotland's benefit in a partnership of four nations.

At the same time, we have a Union in which national identities can flourish and be celebrated.

I want Scotland to have a stronger Scottish Parliament while retaining full representation for Scotland at Westminster.

The benefits of our combined resources would be lost in the event of independence.

By contrast, a promise to ensure Scotland can take more responsibility for money raised and spent here means we can tackle Scottish problems in Scotland without the huge uncertainty caused by a vote for separation from the United Kingdom.

ON the one hand, we can have further devolution, helping to strengthen our union.

On the other, the complete break championed by the SNP would leave us isolated and facing uncertainty.

Independence is a leap in the dark. We simply don't know what life in a separate Scotland would look like.

With a promise for increased powers for the Scottish Parliament, we can take more responsibility for governing ourselves while still benefiting from our historic partnership with the rest of the United Kingdom.