Colin Conn could very well end up with a crick in his neck. He has been driving around Belfast, spire spotting. Not any old spire, you understand. It's the Spire Of Hope, now mounted on top of St Anne's Cathedral and soaring 72 metres into the blue, that the Belfast architect can't take his eyes off.

"I'm enjoying seeing it from different angles, playing 'spot the spire' ... coming down the Newtownards Road, coming in from the M3, down the Shankill Road, up Joy Street from Ormeau Avenue."

Belfast's skyline changed forever with its erection one workaday Tuesday morning.

Being Belfast, the invitations said 'weather permitting'. Traffic stood still, breaths were held and, yes, the weather was kind as a new piece of the city's architectural history slotted neatly into place.

The sun shone on the impressive 40 tonne stainless steel and glass structure - the joint creation of Conn and fellow architect Robert Jamison - as it was hoist gingerly into position.

It was a momentous day in the history of the Cathedral, with the spire finally completing the building, after a century of waiting. And, love it or loathe it, the new spire creates a landmark piece of architecture in an area of the city already bringing in new business and tourism on the crest of a sea change.

New era

In terms of timing, it couldn't have been better, with the Spire Of Hope reflecting a new era of prosperity and political stability in the city. And already it's attracted nearly as much media attention as a photocall for a handshake between Messrs Paisley and McGuinness.

Again, this being Belfast, it won't be long before the spire - like the Doll on the Ball - has a nickname. Suggestions on a postcard, please.

Aesthetically, it won't be everybody's cup of tea. Some see it as "drawing the eye upwards towards light and eternity".

Others might be reminded of a Glass Slipper on an Ugly Sister. Or a hatpin on a bowler. A needle on a haystack. I couldn't possibly comment. But it's bold, brave and dramatic and it's here to stay.

It's been a lengthy project. An architectural competition was launched in 2004 to design a spire for the Cathedral. Colin Conn and Robert Jamison, as part of the team from Box Architects, were winners of the contest and have worked closely with the project team over the past three years to ensure the successful implementation of the design concept. The two have gone on to form their own practices, Colin Conn Architects and Robert Jamison Architects.

The spire is one of several regeneration projects that the architects are involved in and which are helping to change the face of Belfast. They both collaborated on 'The Potthouse' in the Cathedral Quarter and Colin Conn is currently working on a series of other projects which will further redevelop the area including a £15m, 170 bed hotel and 30,000 sq ft office space. The mounting of the spire was, in every sense, a landmark day.

As Colin's father Eric Conn, a writer, put it in a congratulatory email to his son: "This was a time when they all learned to live in peace.... it was a day when the trivia of everyday life was suspended while I watched the team put down a marker for history."

Colin sees Belfast as poised for success: "It's now Belfast's time. Finally it's here. It's finally started to happen. In 1997, when I first came back to work here, the whole city centre was carved up by massive roads and empty space. It was a city of car parks. Like a doughnut - with no centre. Slowly but surely the urban fabric is being repaired. A city can only develop from the inside out."

It started with Laganside when the city turned and embraced the river on which it had once turned its back.

Current development of the Cathedral Quarter is at the core of this drive, he believes. "The Cathedral Quarter is where the city began - right on the four corners - and that's where the city is now being regenerated."

Of the hotel development, he adds. "We've retained the existing Victorian facade. There's a new street running through it - a new cobbled lane which connects to the existing laneways which are very important to the character of the Cathedral Quarter."

Blending old and new together is key here, he insists - restoring existing buildings, while "making the whole thing feasible by adding value with modern 21st century architecture which makes the project work economically".

But, hold on a minute. Isn't that the sort of thing to provoke a Prince to cry "carbuncle" ? Have Conn's designs attracted criticism? "All the time. I do welcome debate! First and foremost, I'm very much a modern architect and I believe architecture should be contemporary, that it should be consistent with its time. I don't believe we should be looking back to the Victorians, Greeks, Romans or anybody else.

Modern architecture

" They were all modern architects of their time. We should produce modern architecture of our time. And we should look to progress existing architecture.

"We had this debate in the planning process for the spire. The spire is very contemporary and it sits on a 100-year-old building. Rising elegantly from 20m above the Cathedral floor, through the ceiling and new glass roof, finishing 72m above the ground, it is designed to complement the original design, at the same time emerging as a stand-alone piece, marking the difference between old and new.

" The Cathedral has finally been completed with the addition of this fabulous spire which not only celebrates its 100-year history but also a new era of peace and prosperity for Belfast.

"The spire tapers upward like a needle and due to the stainless steel used in its design it will be illuminated and spotted from miles around. It certainly signposts the Cathedral and places it head and shoulders above the architectural competition in the area."

Robert Jamison adds: "It was crucial for us to create a piece of architecture that was in keeping with the existing building and its dominant features, but also to reflect the positive and exciting changes that Belfast is undergoing, especially in the rapidly developing Cathedral Quarter. The Spire will become a central focus in this area and a soaring inspiration for the future regeneration of Belfast."

Challenging modernity may be all very well in a public space, but what decisions does Colin Conn make at home?

He practices what he preaches. "We live in an 1880s house in south Belfast with a modern steel and glass extension. Our home in Italy - my wife, Bronagh, is half Italian - is a 500-year-old stone building with a geothermal heating system, solar power and various environmental technology integrated into what is a very old structure. I love modern architecture.

"And I also love to preserve the past - without replicating the past. Bronagh, who started Box with me, is an interior designer."

Colin left Northern Ireland, for years at a time, to study and work in Europe and Australia. "My father sowed the seeds of wanderlust within us all."

He is also raising the profile of Northern Irish architecture abroad, with several projects in France, Italy and Spain on the go and schemes such as the regeneration of the Stadtbibliotek in Berlin under his belt.

But he has always come home. "Belfast is somewhere we will always have a base. I've tried to leave Belfast so many times - but it keeps pulling me back. With three young children - Hannah, 10, Patrick, eight, and Ellie, six - we came back for the education, which is probably the best in the world, and for the people and also for the fantastic opportunity Belfast now has.

"I believe that people who do leave here to travel, work or study have so much more to contribute when they come back."

And, equally, was it necessary to leave in order to learn and grow? "I think you have to, especially in architecture. Architecture is every culture in the world. It's your duty to go and see what's happening elsewhere - and bring it all back home."