By Nick Assinder BBC News Online political correspondent

It was a speech marked by one central theme - change.

The Queen addressed both Houses of Parliament in the historic Westminster Hall with a Golden Jubilee speech which sought to encapsulate the age in which we all live.

"Change," she declared "has become a constant. The way we embrace it defines our future".

Tolerant nation

Great institutions are never exempt from such change, but the monarchy, she pledged, would meet that challenge by evolving.

She, however, would continue to rule to the best of her ability throughout the changing times ahead, she pledged.

The speech signalled an awareness that the institution of the monarchy itself cannot remain static if it is to maintain its relevance.

No abdication

It remains to be seen whether that means an enhanced role for Prince Charles.

But it also finally settled the question which has dominated talk about the monarchy's future since the death of the Queen Mother.

No abdication for Charles

Whatever else may change, Queen Elizabeth II is not going to abdicate.

Her words painted a picture of a country whose institutions and character have enabled it to weather all the momentous events of the past half century.

And reference to the fairness and tolerance of the British people combined with the growth of a tolerant, multi-cultural and multi-faith society, appeared to be a direct rebuff to the far-right extremists who often claim only they represent the true British character.

With the shock electoral success of Jean Marie Le Pen in France and fears of a BNP revival in Britain, it was a timely reminder of the natural tolerance of the British nation.

Survived war

The setting for the speech - the ancient hall which has witnessed some of the most dramatic and poignant events in the country's history - could not have been more appropriate for such a message of change.

Just a few weeks ago her mother lay in state only yards from where she spoke.

Queen Mother lying in state

And, virtually at her feet, was the spot where Charles I was sentenced to death.

The trials of Sir William Wallace, Sir Thomas Moore, Guy Fawkes and the rebel Scottish Lords all took place here.

Its arching, hammer-beam roof and spectacular stained glass window looked down on Coronation feasts from Stephen to George IV.

Unlike other parts of the palace, it survived war - but required extensive repairs between 1914 and 1923 after being infested by death-watch beetles.

Stuff the jubilee

And the half century during which the Queen has ruled has been as momentous, and often bloody, as any age before it.

Even 25 years ago, during her silver jubilee, Britain was a country far from at ease with itself - or even its monarchy.

Industrial and social strife was endemic and the "stuff the jubilee" movement struck a chord, particularly with disaffected youngsters.

A quarter of a century later and things look hugely different. Britain is far from trouble-free, but it appears a distinctly calmer place.

The Queen clearly felt relaxed, even confident, about her own position and the future of the institution.

Outward looking

Republicanism may be a more respectable policy than it was 25 years ago, but there were no hints here that the Queen senses any growing desire to abandon the monarchy.

If anything, events of the past few years appear to have strengthened its position, allowing the Queen a more relaxed, outward looking view.

Speaker's words of tribute

And one overwhelming message was delivered back to her from MPs, Palace of Westminster staff, Lord Chancellor Derry Irvine and Commons Speaker Michael Martin - two people from opposite ends of the class system.

It was that they see the monarchy as a unifying point of reference in the changing world.

Fifty years on, and this monarch looks as secure and as central to British life as any before her.