With song, confetti, balloons, tears, some words of defiance and a few laughs, the £50 million Reid Building at the Glasgow School of Art has been officially opened.

The words of the song were provided by an alumni of the GSA, the Makar Liz Lochhead, the laughter and tears by former student and now world-famous actor Robbie Coltrane, and the defiance by Steven Holl, primary architect of the stark, modernist structure that stands opposite the Mackintosh Building in Garnethill.

The New York architect felt some of the critics of his exterior design should now visit the building, "an homage to Mackintosh", and change their minds.

Mr Holl said: "It was a difficult project. We had a lot of controversy there were some suspect articles from people second-guessing what this building could be, and I am very excited that people can come inside of it.

"You must come in, walk the space, and that is really when you feel the space and the energy.

"I think the students 100% get it, and I think the people who have been in it get it, but I would like to see those early critics come inside."

Coltrane, 64, who walked with a cane because of a painful leg, said generations of future students would love working in the "glorious building".

The actor studied at Glasgow School of Art when he was known by his birth name, Anthony McMillan.

He said: "There are painting tutors long dead burling in their graves right now. 'Are you telling me that cheeky little b****** McMillan, with his hair down to his arse and a permanent joint in his mouth, who said film was the future, is opening the new building opposite the 'Tosh?'"

"You walk into this building and you are overcome by that sense of awe, your breath is taken in, it is so beautiful, those flumes, that big curvy wall, which I was going to say it looked like Carol Vorderman bending over, but my son told me that was old-school and sexist,' say that it looks like a 1956 Cadillac bonnet' - so you can choose.

"I remember walking around the Mackintosh and thinking it was going to raise my game, because some bastard sat down with a pencil and paper and drew this building, and Glasgow built it, Oor dear Toon."

He added: "The most important thing is the impulse to make things: people who make things cannot help themselves.

"I don't do much drawing any more, and my paintings you would be embarrassed to see, but I do make movies and TV, and this glorious building is going to be the place to encourage that and many beautiful things will be made here, and you should all be proud."

The GSA choir stood on the interior steps of the new building and sang Making It New, with words from Lochhead, who studied painting at the GSA.

Students, primarily studying design, have been working in the building since January, but now its construction is complete.