By Simon Morris BBC News

The Senedd, the Welsh assembly's debating chamber in Cardiff Bay

A timid measure... or the most extraordinary change since the Act of Union in 1536? Two recent descriptions of the Government of Wales Bill, due to get royal assent on Tuesday.

So which is right? Given the piecemeal, incremental nature of Welsh devolution it could of course be both.

The whole point of the new legislation is to give the Welsh assembly much greater scope to pass laws for Wales without having to go through Parliament. But first the Welsh Assembly Government had to get it through Parliament itself.

That meant winning over openly sceptical Welsh Labour MPs. So when he was at the despatch box in Westminster, Welsh Secretary Peter Hain had to reassure them they would still be in charge.

And of course he was right.

Parliament remains sovereign and can still stop the assembly in its tracks or even abolish it. But when he's in Cardiff Bay Mr Hain talks about a new dawn for devolution, the most significant transfer of power since the assembly opened for business in 1999.

The precedure allows the assembly to take the initiative far more

Rhetoric maybe, but also containing a large dose of truth.

The explanation for this apparent paradox can be found in the complex procedure the new Government of Wales Bill sets up. The procedure allows the assembly to take the initiative far more.

The parliamentary stage is much faster and simpler. And the end result will be to let the assembly pass its own laws or repeal laws passed at Westminster.

Those are all, in Mr Hain's phrase, "significant transfers" of power. But the procedure can only be triggered if he agrees.

MPs and peers have to give their approval, and the areas in which the assembly can pass or repeal laws could be tightly restricted. That's how Parliament remains "in charge."

Back of the queue

Say, for instance, the assembly government wants to make a law requiring gas, water and electricity companies provide services in Welsh and English.

Previously, that would have needed MPs to hold three debates and do clause-by-clause examination of the bill. Then peers would have to do the same thing all over again.

The Westminster government might well have more pressing concerns and be reluctant to give the issue all that parliamentary time. So the bill would keep going to the back of the queue and might never see the light of day.

Under the new procedure the assembly government will ask the secretary of state to lay an order before Parliament giving the assembly power to make the new law.

MPs would debate it only once, for 90 minutes, peers likewise. Assuming it was approved, the rest would be up to the assembly.

One MP described it as 'salami slicing power' away from Westminster, which is not a bad description

Depending on how broadly the order was drafted the assembly could then have power to make laws affecting large areas of language policy without ever having to go back to Parliament.

In that way the assembly should gradually accumulate more and more freedom of action.

One MP described it as "salami slicing power" away from Westminster, which is not a bad description.

What happens if Parliament blocks the assembly's wishes? That's unlikely to happen.

The British constitution relies on conventions, in this case something called the Salisbury convention. That means Parliament shouldn't block any manifesto commitment by a ruling party in the assembly.

But if it does, then the assembly has a nuclear option. The Government of Wales Bill allows it to hold a referendum on full-blown law-making powers for Cardiff Bay, provided two-thirds of AMs agree.

Since that effectively gives Labour a veto on whether the referendum option should be used, it's clearly aimed at a situation in which a Conservative government at Westminster stands in the way of a Labour-controlled assembly.

There's a growing sense of inevitability about full law-making powers, though maybe not for a good few years yet.