Boris Johnson is set for a triumphant appearance on the Tory conference platform amid speculation about his leadership ambitions.

The London mayor revelled in a hero's welcome from activists when he arrived at the gathering in Birmingham on Monday night.

But in his keynote address he will again insist he is completely loyal to David Cameron, praising the Prime Minister for taking "difficult decisions in difficult times".

The public statement of support comes after the party leadership made a series of announcements seemingly designed to soothe restive right-wingers.

Chancellor George Osborne unveiled plans for workers to sacrifice employment rights in return for shares, and confirmed that he wanted to slash another £10 billion from the welfare budget in 2015-16. Meanwhile, new Justice Secretary Chris Grayling is pledging to strengthen legal protection for householders who attack burglars.

In extraordinary scenes, Mr Johnson was mobbed as soon as he stepped off the train in Birmingham, with passers-by chanting "Boris! Boris!" as he fought his way through ranks of TV cameras and photographers. More than 1,000 activists turned out for a fringe event where he insisted he would continue to speak his mind on key policy issues such as Heathrow Airport expansion.

However, he stressed that such tensions did not mean he wanted to take the Prime Minister's job. "It is sometimes inevitable that the mayor of a great city will find himself saying things that do seem at variance with national policies," he said. "Of course I am going to continue to lobby for a long-term solution to our aviation capacity problem. No one as a result should have any cause to doubt my admiration for David Cameron."

He stressed he was one of the first "Cameroons" in the 2005 Tory leadership contest. "I believe that in tough circumstances he, George Osborne and the rest of the Government are doing exactly what is needed for this country and to clear up the mess that Labour left."

The event was given the tagline "Re-elected and Olympotastic", and began with a video describing his poll victory this year as "Mission Imborisable".

He was greeted with a standing ovation, and repeatedly drew cheers with a joke-laden speech. Answering questions from the audience, he contradicted party policy by indicating he wants a return to a grammar school-style education system. "I personally have no objection to selective admission at some stage in a child's development," he said. "Thankfully, I suppose, for the party policy I'm not in a position to do this."