Council meeting:The British and Irish governments have stressed a fresh commitment to security and to developing co-operation across the EU.
In the wake of the attacks on London and at Glasgow airport, the Taoiseach and the prime minister marked the holding of the British-Irish Council at Stormont with pledges to consolidate the fight against international terror and against organised crime.
"It is an area where it is in everybody's interest to fight against crime, to fight against drugs and fight against organised criminals who make vast amounts of money," Mr Ahern said.
The Taoiseach, meeting the new prime minister for the first time in Belfast since the departure of Tony Blair, held a bilateral meeting in advance of the Stormont talks which involved the devolved administrations of Northern Ireland, Scotland and Wales as well as representatives from the Isle of Man and the Channel Islands.
"Anything we can do about harmonising rules and regulations that make that more efficient all the better," he said. "In Europe generally more effort has to be put in." Mr Ahern and Mr Brown pledged to work for deeper co- operation on a range of EU issues.
The two also committed their governments to sharing security information and to progress on biometric passports.
Questioned about funding arrangements for the Stormont executive, Mr Brown said final details were still being worked on and would not become clear until the completion of the comprehensive spending review in the autumn. However he said that £51.5 billion (€75.4 billion) was currently available for investment in large-scale infrastructure projects.
"The financial package is very big indeed - £51.5 billion over the next few years," he said. "It is to make possible the current expenditures of the Northern Ireland Assembly and to make possible a big programme of investment in the future."
Mr Brown, like his predecessor, travelled to Northern Ireland within a month of taking office at No 10 to meet the Taoiseach. He later left Stormont for his first foreign meeting in Germany with chancellor Angela Merkel.
Mr Brown said he was particularly pleased to visit Stormont as the new executive was settling down to business.
"I believe that we have entered into a new historic time for Northern Ireland," he said.
Mr Ahern and Mr Brown were received at the doors of Stormont by First Minister Ian Paisley and Deputy First Minister Martin McGuinness.
Dr Paisley, who last month warned that the prime minister should attend the British-Irish Council otherwise he would not be there, placed considerable store on the convening of the representatives from across the UK.
"This is a very important meeting and to have all of the leaders of these various governments with us today, including our new prime minister," Dr Paisley said, "is really a bonus for Northern Ireland. We are not any longer on the periphery, we are in the centre."
On the unfinished business of a financial package designed to meet Northern Ireland's severe infrastructure problems, Dr Paisley added: "That is a task that we have to take on, both myself, the deputy [ Mr McGuinness] and the other members of the government here."
Mr McGuinness said: "All of this is a work in progress, but the prime minister was at pains to say that he is here to help and that he recognises the economy is of critical importance."
Ministers from the Government and the Stormont executive meet in Armagh today under the North-South Ministerial Council to discuss a range of cross-Border projects and subjects of mutual interest. Both the conference and the council are part of the measures introduced under the Belfast Agreement.