GORDON Brown has agreed in principle to increase British troop numbers in Afghanistan to 9,500, he told the Commons today.

The Prime Minister said the rise of an extra 500 service personnel would depend on three conditions being met.

First, an Afghan government commitment to put forward sufficient new troops to be trained; second, that all units could be properly equipped for the task; and third that the increase was part of a coalition-wide deployment with each ally bearing its fair share.

Mr Brown said the UK would also provide an extra £10m in humanitarian assistance for areas of Pakistan liberated from terrorist control.

He told MPs he regularly questioned whether sending British Armed Forces to fight on the other side of the world could be justified.

"I have to conclude that when the safety of our country is at stake, we cannot and will not walk away," the Prime Minister added.

Tory leader David Cameron welcomed the statement but called on Mr Brown to make clear whether the additional troops would be sent from the UK or be soldiers who were having their deployment extended.

And he asked the Prime Minister to make clear whether military commanders had actually requested 2,000 extra troops, adding: "Don't you understand we are only going to carry the public's confidence if we are straight with them about the choices that we face."