The chancellor of the exchequer and his ally, Trade and Industry Secretary Alistair Darling, were to depart for the sub-continent Tuesday lunchtime (1300-1400 GMT) with senior British political reporters in tow.

Although the trip is mainly focused on strengthening bilateral trade links, analysts see Brown's visit as key to preparing the ground for and gaining experience before his expected promotion to the top job later this year.

Brown -- best known for his careful stewardship of the British economy -- is widely seen as the man most likely to take over when Prime Minister Tony Blair leaves office within the next nine months.

In recent weeks, he has strayed beyond his Treasury department brief in a series of high-profile appearances and speeches, to demonstrate his grip on wider policy issues and win over public opinion.

They have ranged from domestic issues like education and health to foreign policy, in particular Britain's controversial presence in Iraq, to give a flavour of his future premiership.

Brown and Darling -- who is himself being tipped to take over the post of finance minister -- are being accompanied to Mumbai, Delhi and Bangalore by more than 150 business leaders from more than 80 British companies.