I am 35,000ft above Afghanistan. Beneath me, in the snowy hills, an insurgency is raging. In front of me sits David Miliband, Britain's foreign secretary, who is leaning forward in his cream-coloured leather seat on a flight from Kabul to Dhaka, the capital of Bangladesh.

''Amartya Sen is a brilliant man,'' remarks Miliband. ''I think his argument that there is a fusion tradition - a liberal tradition that is concerned with social justice - is right. And I admire his work on capabilities, and on freedom as capability.''