A defiant Gordon Brown has dismissed growing turmoil within the Labour Party over his tax reforms as he moved to cement the "special relationship" with America.

Standing alongside President George Bush in the White House Rose Garden, the Prime Minister brushed aside concerns over the scrapping of the 10p tax rate.

"I am sticking to the job and getting on with the job," he told reporters.

Instead he sought to focus with Mr Bush on a push for new international sanctions on Iran over its nuclear enrichment programme while heaping praise on the president, who leaves office next year.

"The world owes President Bush a huge debt of gratitude for leading the world in our determination to root out terrorism, to ensure there is no safe haven for terrorism and no hiding place for terrorists," he said.

However, Mr Brown was also looking to the future, taking the unusual step of meeting the three contenders to succeed Mr Bush - Democrats Hillary Clinton and Barack Obama, and Republican John McCain.

"I am absolutely confident that through working with any of them we could rise to the great challenges of the future," he said.

The body language between Mr Brown and Mr Bush was noticeably warmer than at their first meeting last July at the presidential retreat, Camp David.

However, it could not disguise the fact that his visit had been eclipsed in the US by the visit of Pope Benedict XVI while in the UK it was overshadowed by his troubles at home.

As Mr Brown's motorcade swept into the White House, it was cheered by a small knot of spectators who apparently thought that it was bringing the Pontiff.