The tribute will cost �3m and open next year

A ceremony was held on Wednesday to mark what is seen as an important stage in the creation of the tribute, in Hyde Park, central London.

The �3m fountain and surrounding gardens will be formally opened in the summer of 2004.

Designed by American architect Kathryn Gustafson, the fountain is based on a large oval stone ring.

The final design for the permanent memorial, being built next to the Serpentine, was chosen to reflect the life of the Princess.

Work began on the project in June of this year.

A few months delays will seem very insignificant in the context of a very very beautiful place Culture Secretary Tessa Jowell

The first jobs included removing the topsoil, laying the foundations and installing the fountain's pipe work.

That will be followed by the assembly of the stone sections and the restoration of the surrounding parkland in Spring 2004.

Once the fountain is completed, visitors will see what backers describe as "an extraordinary water feature".

Ms Jowell said there had been two major hitches in getting the project started.

One was because the original site was revealed as a site of Roman remains, she explained, and the second was due to the "technological challenge" of cutting all the granite required for the fountain.

"These are reasons why it has taken longer, but remember this is going to be here for hundreds of years and I think that as generations long after us look back a few months delays will seem very insignificant in the context of a very very beautiful place."

'Rocks and rolls'

A stone oval 210 metres in circumference will be formed, over which water will "run, tumble, cascade, curl and bubble before finally coming to rest in a large, tranquil pool".

Water will pour into the structure from the top of a hill at the Serpentine Bridge and run in two directions.

In one direction it forms a tight, fast-flowing torrent, creating water jets.

In the opposite direction it forms a dish that "rocks and rolls" water through a more slower incline.

At night the shape, which can be planted with plants and trees, will be lit up.