The cabinet later got together at the SWALEC Stadium for the government's first cabinet meeting in the Welsh capital.
WRU Group Chief Executive Roger Lewis, who welcomed the Prime Minister to the home of Welsh rugby said, "While we have an excellent relationship with the Welsh Assembly Government, it is equally important to meet UK leaders such as Prime Minister Gordon Brown and his cabinet members, who have an important role to play where Welsh rugby and the Millennium Stadium is concerned.
"I thanked Gordon Brown for his role in England's bid to host the 2015 Rugby World Cup, underwriting the bid to the sum of £25 million. If that bid is successful, it would bring two quarter-finals and five Pool games to the Millennium Stadium which would greatly benefit Cardiff and South East Wales economically. Equally, we are looking forward to hosting 15 soccer games in the 2012 Olympics, which will ensure Wales plays a part in the London event.
"The Prime Minister was very complimentary about the Millennium Stadium, and was well aware of the activities that have taken place here, being a keen follower of rugby and a former player himself. We discussed the benefit the Millennium Stadium brings to Cardiff and South East Wales not only through sporting occasions, but also with major concerts and other events and as we celebrate its tenth birthday, Mr Brown recognised the stadium as the most successful Millennium Commission project."
Meanwhile Wales stars Andy Powell and Matthew Rees joined Foreign Secretary David Milliband and First Minister Rhodri Morgan at the Senedd to discuss the recent tour to South Africa and their off-the-field experiences of the nation and its people.
The players told guests at the reception how they visited townships and helped raise cash for a children's charity in South Africa during the six week long tour.
Andy Powell said: "I paid one visit to the Alexandra school in Johannesburg where we helped with training and handed out some of our spare kit to the youngsters.
"It was quite emotional witnessing some of the living conditions but the experience was extremely positive and I think it is important for us to help in that way."
Matthew Rees explained to the politicians how he had chaired the tour's light-hearted Fines Committee which raised cash from players and coaches for minor misdemeanours like being late for a training session. They eventually handed more than £3,000 to a charity which helped children in South Africa who are HIV positive.
Rees said: "We had some fun collecting the money, but we wanted to make sure it was contributed to a worthy cause which would be of genuine help in South Africa."
The politicians were told how community visits and activities now play an important role in tours to South Africa, and links with South Wales based charities such as Valleys Kids with links to South Africa now feature in match and tour build-up events.
David Milliband said: "It is nice to hear from the players of the importance they placed on off-the-field activities which get them involved in community life in South Africa."