Professor Peter Higgs has revealed he was quietly enjoying a lunch of soup and sea trout in Leith when the Royal Swedish Academy of Sciences announced to the world he had won the Nobel Prize for Physics.

The academy had tried to contact Mr Higgs in advance, but had been unable to reach him.

The academic only discovered he had won the most prestigious prize in his field when he was walking along Heriot Row in the New Town of Edinburgh.

A former neighbour, the widow of a judge, got out of her car and stopped him in the street. "She congratulated me on the news and I said 'oh, what news?'" Mr Higgs told a press conference at Edinburgh University. "She told me her daughter phoned from London to alert her to the fact I had got this prize.

"I heard more about it obviously when I got home and started reading the messages."

Speaking for the first time since he was awarded the prize, the 84-year-old grandfather said: "How do I feel? Well, obviously I'm delighted and rather relieved in a sense that it's all over. It's been a long time coming."

He had heard from a friend he was first nominated for the prize more than 30 years ago.

Mr Higgs was awarded the prize, along with Belgian physicist Francois Englert, for his pioneering work as a young lecturer at Edinburgh University in 1964 on a theory about the existence of a particle that gives other fundamental particles their mass, the so-called Higgs boson.

The Large Hadron Collider at the nuclear research facility (Cern, originally Conseil Europeen pour la Recherche Nucleaire) in Geneva, Switzerland, was built largely in order to test the theory and in July 2012, scientists announced they had found a particle consistent with the Higgs boson.

The professor, an appreciator of beers, toasted the triumph on a flight home from Cern with some London Pride, and was presented with a bottle of the beer during yesterday's press conference by his friend, physicist Alan Walker.

Mr Higgs said he had celebrated his Nobel Prize on Thursday night with friends after a lecture by the particle physicist Professor Frank Close of Oxford University, but that was only the beginning: "I shall be celebrating with my family with the help of a bottle or two of champagne early this evening," he said.

The prize has cemented international celebrity for a man who does not seek the limelight and has only recently acquired a mobile phone. Facing dozens of photographers and journalists in the university's grand Playfair Library, the jacketless professor seemed relaxed, but, flanked by the university's principal, Professor Sir Timothy O'Shea, and Tait professor of mathematical physics, Professor Richard Kenway, admitted to misgivings about his global celebrity.

He said: "I think I face the immediate future with some foreboding because having experienced the wave of attention which followed the announcement at Cern in July 2012, I anticipated this last announcement will trigger an order of magnitude of more attention.

"I think I am going to have difficulty in the next few months having any of my life to myself."

Mr Higgs - who admitted to preferring chemistry to physics at school and being better at it - was at pains to share the credit for his discovery with other scientists who had worked on the theory, saying: "I should remind you that although only two of us have shared this prize, Francois Englert of Brussels and myself, that the work in 1964 involved three groups of people, (including) two in Brussels.

"Unfortunately Robert Brout died a few years ago so is no longer able to be awarded the prize, but he would certainly have been one of the winners if he had still been alive.

"But there were three others who also contributed and it is already difficult to allocate the credit among the theorists. Although a lot of people seem to think I did all this single-handed, it was actually part of a theoretical programme which had been started in 1960."

He said the work on the Higgs boson would go on. For himself: "Obviously I have to start thinking about a trip to Stockholm."

l The Scottish Government is to support the creation of a home for the recently established Higgs Centre for Theoretical Physics at Edinburgh University, it was announced yesterday. The centre will "nurture new generations of physicists" and bring together scientists and industry representatives.