Tory conference: The politics of succession

The prime minister watched the chancellor on stage yesterday like a proud father on the touchline, as George Osborne unashamedly spelt out his pitch to the "common ground" of British politics.

But the mood couldn't have been more different at the conference today as the home secretary gave the toughest Tory speech on immigration this audience has heard for years.

Theresa May claimed that the high immigration of recent years has been "corrosive", new arrivals have taken British jobs, and announced a new system to crack down on asylum. The audience gathered in Manchester lapped it up.

But the speech left the prime minister struggling to avoid contradicting her. He told me she is right but he also tried to deflect some of her bolder claims that many in the government don't accept, for instance that immigration is of no benefit to the economy.

He also sought to contain the strangeness of the home secretary criticising her own department and government's failures to stick to its ambition of getting immigration down.

There is double trouble here tonight, because as the PM admitted to me the government's policy "hasn't worked so far". Criticism from his own home secretary has forced him on to the back foot, having to defend what they have achieved, or rather not achieved.

And because David Cameron set his own trap, setting a target in 2010 and again in 2015 to bring immigration down to the tens of thousands each year, a level it hasn't been at since 1997 and a level that the UK's membership of the European Union makes extremely hard to meet.

But the other issue that's impossible to ignore is why Theresa May chose to make such a tough speech today. Ambition. She wants to stay in the race to be the next Conservative leader. After George Osborne's performance yesterday, and his increasing mastery of the party, she doesn't want to be edged out. A hard line speech on immigration is an attempt to put herself back on the map.

And she was followed on the platform by Boris Johnson, who with a very different tone, a very different speech, was doing exactly the same thing, trying to get back in the race.

He entertained the crowd as ever. But there a was a deliberate attempt in his speech to show what he has delivered in his time as Mayor of London. He wants to answer the criticism that he's simply not serious enough to be the next PM. And he's had a good day here. The prime minister even told me he'll offer him a job in Cabinet when he leaves City Hall.

The current prime minister told me he is simply delighted to have a such a strong team, suggesting it doesn't bother him that there is so much focus already on who will take over.

But it's another trap he set himself when he decided to be candid about his own plans to leave. Many people here in Manchester are now preoccupied with who comes next. For a government that's trying to deliver, it's perhaps a distraction it does not need.