By John Pienaar Chief political correspondent BBC Radio Five Live

Tony Blair has reached the age where it is appropriate for his name to appear - apparently without his permission - in an advertisement for Sanatogen.

It might have been worse. As he told a lunch gathering of editors and newspaper proprietors, he has not yet followed the football legend Pele and started promoting the benefits of Viagra.

Polls suggest the Labour leader is more popular than his party

Like it or not - and he confessed to Saga magazine he was dreading his 50th birthday - Mr Blair seems to have been dragged into a moment of introspection.

Where prime ministers are concerned, these arbitrary dates in the calendar tend to take on artificial importance.

So, has Tony Blair yet drafted a hugely impressive entry of great distinction in the history books?

The answer is probably no, or at least not nearly as impressive as he would wish.

True, two consecutive landslides (the pollsters seem confident of a third) have broken new ground for a Labour leader.

He is also, the youngest prime minister in a couple of centuries.

But achievement between elections is what truly matters, and these are still mostly works in progress.

Man of conviction

Memories of the Iraq war are still very fresh.

That surely counts as a work in progress, and, on Mr Blair's own admission, will continue to be one until progress is made bringing democracy to that country and some kind of peace and stability is brought to the Israel-Palestinian dispute.

Two landslide elections broke new ground for Labour

As things stand, Mr Blair has earned new respect as a man of conviction; no longer obsessed by focus groups and opinion polls.

And he has shown he is prepared to take on his party in the hope of winning an argument with the public.

That helps to explain his approach to the introduction of foundation hospitals, NHS reform and the overhaul of public services which will in the end define his political legacy.

The latest batch of opinion polls suggest Mr Blair may have regained his status as a leader more popular than the party he leads.

While that continues to be true, his will be a strong position.

Many Labour MPs, who value their ideological roots value their seats in Parliament still more.

They will follow, however reluctantly, where Mr Blair leads.

Sweeping reforms

We should not overlook some dramatic developments.

The constitutional reforms; the Scottish Parliament and Welsh Assembly, incorporating the Convention on Human Rights into British law; clich�s about "historic" change are, for once, appropriate.

Then, there is the small matter of establishing a reputation for economic competence for a party conventionally considered economically feckless.

Labour and perceptions of Labour have been transformed.

But reforming public services still stands as the ultimate test of the Blair premiership.

And while reforming the services will be one thing (and a very difficult thing) producing visible and undeniable improvements will be something else.

Both challenges remain to be overcome.

The key entry in the history books has not yet been written.