Published Thursday, 18 June 2009
The Prime Minister was speaking at an EU summit which is due to approve written pledges to Irish voters that the Lisbon Treaty will not affect Irish tax policy, neutrality, abortion laws or workers' rights.
The guarantees are seen as vital if an Irish "no" to the Treaty last year is to be overturned in another referendum in the autumn.
On the eve of the summit Taoiseach Brian Cowen wrote to Mr Brown to ensure British backing.
"Britain wants to see a solution to the problems of Ireland and the concerns in the letter", Mr Brown replied.
"The important thing is that we make sure we do the right thing by Ireland and by Europe.
"I want to ensure that the Lisbon Treaty as it affects Britain will not be changed in any way."
Hopes are high in Brussels that the guarantees will be approved, reinforcing recent poll figures showing a majority in Ireland are now ready to vote to approve the Lisbon Treaty.
But Czech President Vaclav Klaus has signalled that the changes planned for Ireland may mean that Czech ratification will have to be looked at again.