Another win will prove Boris Johnson really is a big beast for No10 to be scared of

For someone contemplating his future as a big beast in the political jungle, it was perhaps apt that he was gazing at lions and leopards in the Ruaha National Park in Tanzania.

Although he has for months been increasingly keen on a re-election bid, aides say the holiday offered the Mayor the time to ponder on the successful launch of his new bike scheme and on his overall progress at City Hall. Crucially, it also allowed him to confirm the full backing of his wife Marina.

One powerful factor was internal polling that showed that his satisfaction rating among Londoners was still high. More than two years after he ousted Ken Livingstone, the "Boris honeymoon" appears to be continuing.

But even though he has today "knocked on the head" any lingering doubts about whether he'll stand in 2012, the next, inevitable question is this: will Boris serve a full second term or will he find a way back to national politics and No 10?

For the time being, David Cameron will be relieved that one of the most popular Tories in the land is staying in London. Although tensions will continue over the Mayor's outspoken warnings on immigration policy and spending cuts, nervous advisers in Downing Street can breathe more easily that Boris is keeping away from Parliament for the foreseeable future.

One friend of the Mayor said today that he expects him to answer tricky questions with a "Tony Blair-style" pledge that he will "stand for a whole term". "He would never be interested in going back to Parliament to be a backbencher. If he goes back, it would be for a very big prize and it would only ever work if he'd made a success of the job in London.

"In turn, that means winning a second term on his record and hosting a fantastic Olympics — then he would be an extremely strong politician in any scenario. He'd have provenly his popularity and be taken seriously."

Serving a full two terms would certainly confirm that new seriousness. There is, however, also a very practical reason preventing any thoughts of quitting mid-term, say ahead of the 2015 general election.

It would cost London £10 million to hold a by-election for Mayor: not a cost any "wastebusting" politician would want.