LONDON — After a decade of waiting on the sidelines, Gordon Brown is about to get his big break.The taciturn treasurer, credited for much of Britain’s recent economic boom, is almost certain to become the next prime minister by the end of June, when Tony Blair steps down.

Often described as dour, Brown has been criticised for everything from his dandruff to his alleged “Stalinist ruthlessness.”

But he is largely an enigma, with little known about his political leanings.

He has close ties to Democrats in the United States and is said to be particularly close to Sen. John Kerry, D-Massachusetts.

“I don’t think we’ll see true Brown until the general elections,” said Anthony Seldon, a biographer who has followed both Blair and Brown.

General elections aren’t expected before 2009, which will spark a vicious fight between Brown — a rumpled intellectual — and David Cameron, the fresh-faced leader of the Conservatives who has been compared to the younger charismatic Blair.

He once promised to “spend what it takes” to disarm Saddam Hussein and will likely keep British troops in Iraq for the near future. He will also probably try to maintain a strong relationship with Washington.

Former Cabinet Minister Charles Clarke called the 56-year-old Brown a “control freak” last year. Andrew Turnbull, the former head of Britain’s civil service who broke a customary code of silence, said Brown has often belittled his colleagues.

Brown and Blair both won their Parliament seats in 1983, and it was the beginning of a long and often bitter rivalry for the pair known as the “Odd Couple.”

The two found themselves sharing an office in Westminster. Immediately, they spotted each other’s strengths.

When Labour Party leader John Smith died of a heart attack in 1994, both men were considered for the job.

Political lore has it that the men, while dining at a trendy north London restaurant, struck a deal that stipulated Blair would take over as party leader on the condition that Brown would get control of the Treasury. Blair was then to step down halfway through his second term to make way for Brown as Britain’s prime minister.

That never happened.

Brown’s days in waiting were immortalised in “The Queen,” last year’s film that focused on Blair and Britain’s royal family in the aftermath of the death of Princess Diana. In one scene, Blair is in a meeting when an aide rushes in and announces, “Brown is on the telephone.”

“Tell him to wait,” Blair says.

British newspapers have been saturated with rumours of squabbles between the two.

While Blair initially supported the notion that Britain could embrace a common European currency, Brown quickly shot down the idea, establishing a multifaceted test to show that the British economy would surely suffer.

Blair, needing Brown’s backing, quickly dropped the notion.

Few could ignore Brown’s economic mastery or political ambition.

He started canvassing for the Labour Party at age 12 and graduated from Edinburgh University in Scotland with a doctorate. His thesis was on the links between the Labour Party and Scottish trade unions, according to Robert Peston, author of the 2005 book “Brown’s Britain.”

Brown stuck to Labour’s 1997 pledge to freeze income taxes. He increased government expenditures.

He also pushed for the Bank of England’s independence, credited for Britain’s steady economic boom since World War II.

“I think people will look back on this political partnership and the relationship between me and the prime minister and say well, it is completely unique and you’ve had a chancellor and prime minister who have worked together,” Brown said recently.

Despite economic prosperity, skirmishes trailed Brown and Blair through the decade of their partnership.

In one instance, Brown made it known that he would be sending his son to a public school. Blair sent his children to expensive Roman Catholic schools.

There was also friction between Brown and Blair’s wife, Cherie.

Brown showered Blair with praise during last year’s Labour Party conference when the prime minister said it would be last as party leader.

The compliments, however, were overshadowed by a report that Cherie called Brown a liar. She denied it.

Tragedies have been part of Brown’s personal life.

His daughter, Jennifer Jane, was born prematurely in December 2001 and died of a brain hemorrhage days later.

His son, Fraser, born in July, was diagnosed with cystic fibrosis. He and his wife, Sarah, have another son, John, three.

“I love being a dad. It’s great fun and there’s nothing more important and there’s nothing I enjoy better,” Brown has said.

Gordon Brown the favourite