After a long period in opposition a party chooses a new leader, one man stands aside for his rival on the understanding that if they win the leader will stand down at some point to be succeeded by the erstwhile rival. The other man takes over the economic portfolio and for a while the partnership seems harmonious. After many years in government the Prime Minister shows no signs of standing down and the other man is visibly impatient, supporters of the two men brief against each other but the PM prevails and it is accepted that the departure will be later than originally predicted. More years pass and the Prime Minister appears to indicate that he plans to continue in office even longer than before.
So far this is a description of both British and Australian politics, Blair/Brown and Howard/Costello. Today the Australian Prime Minister announced he was going to contest the next election despite Peter Costello saying explicitly that there was a pact for John Howard to stand down. In Britain Tony Blair has constantly pushed back his departure date as well, leaders don't give up power volutarily they need to be pushed out, unfortunately for Brown and Costello the person doing the pushing usually ends up with nothing to show for it. There are differences between Blair and Howard, Howard is far more popular than Blair and has more leeway but I'm willing to bet that if Labour's poll ratings improve in the next year Tony Blair will announce a similar U-turn and there is nothing Brown can do to stop him without wrecking his own chances of succession.