By Nick Assinder
Political correspondent, BBC News website
Mr Brown's reaction has been unlike Tony Blair's after the 7 July attacks
Gordon Brown could hardly have faced a sharper test of his leadership than the latest terrorist attacks in the UK - quite possibly timed to coincide with his succession.
The way he responds to the crisis, both in terms of policy and his personal style, will help define his premiership even before he has really got into his stride.
Ex-prime minister Tony Blair was noted for his ability - scripted or otherwise - to chime with the public mood and his remarks on the death of princess Diana and the 7 July London bombings appeared to strike precisely the right note for the time.
Gordon Brown is different, and that difference has been striking in his reaction to the latest attacks and the way he has tried to speak for, and to, the nation.
There have been none of the smooth sound bites we have got used to.
In their place has been the sort of solidity and weight, some will say dourness, that have always been the mark of Gordon Brown.
Whether voters will find the change in style refreshing and reassuring or whether they will hanker after the Blair style remains to be seen.
But that reaction could set in stone the public's view of their new leader from here on in.
The prime minister, in his interview for BBC One's Sunday AM, also hinted at a significant change in the policy reaction to the latest events.
His predecessor was unbending in his wish to see detention without charge extended to 90 days, despite suffering a Commons defeat over it, for example.
Mr Brown has insisted, significantly, that this is not an issue for today and that he is seeking consensus.
And he once again insisted he was prepared to call on individuals from any political party or any walk of life to contribute their skills to his policy making, whatever views they may have expressed in the past.
He also notably refused to get into any debate over whether Britain had become a less safe place as a direct result of the Iraq war, insisting there was a global terrorist threat "irrespective" of that, or the action in Afghanistan.
He placed his emphasis on winning hearts and minds and spoke of the possible need for a cold war-style propaganda campaign to pursue that battle.
That again is a significant, if small, shift in emphasis from the former prime minister's approach.
The next few days will show just how well this change in leadership style and approach to policy-making has gone down with voters.
On other areas, Mr Brown delivered a pretty stinging rebuff to his predecessor's style, stating he would be running Cabinet government, not "sofa government".
Bearing in mind his reputation with some people as a "control freak" who brooks no opposition, that is one pledge that will be closely watched.
It will be the clearest possible indication of whether all his talk of change and openness, consensus and involving "all the talents" really adds up to a row of beans, or whether it will be dismissed as spin from the man who said he wanted to end spin.