Anyone wishing to know what Boris Johnson would be like as prime minister should watch his performance in front of the London Assembly yesterday.

Johnson was repeatedly asked about allegations of a "semi-corrupt" relationship between City Hall and developers of London's Royal Albert Dock.

The questions followed an investigation by Channel Four News last week which found worrying links between the mayor's quango London and Partners (L&P) and Chinese developers ABP.

Channel Four discovered that an adviser to the company had donated large sums to the Conservative party in advance of the £1 billion deal. They also alleged that L&P had shared offices with the developers and that one of L&P's employees had later moved over to work for them. They also raised serious questions about the company's human rights record in China.

In unusually frank language, former chairman of the government's Committee on Standards in Public Life Sir Alistair Graham, told Channel Four that the deal had "the smell of a semi-corrupt arrangement."

Whatever the truth of the allegations, they are undoubtedly serious. Unfortunately they were not taken seriously by Johnson yesterday.

Speaking to the London Assembly, Johnson dismissed calls for an independent investigation as "a complete waste of time and money," and insisted that his own internal investigations had cleared the GLA of any impropriety.

In fact the audit report - which was published within minutes of the Assembly meeting beginning - did not even deal with most of the issues raised by Channel Four.

Johnson is often viewed as a likeable 'tell it like it is' figure. But anybody who regularly watches him front of the Assembly will discover a much more slippery character beneath the cuddly facade. Yesterday he was at turns dismissive, aggressive and abusive. Following his questioning on ABP, the Assembly questioned him about leaked plans to cut GLA youth services by 90%. Rather than answer the questions, Johnson dismissed them, telling Labour's Andrew Dismore to "shove it up your…."

Johnson's supporters often highlight such behaviour as a sign of his 'common touch'. In reality it is merely a sign of his increasing contempt for outside scrutiny.

And Boris can afford to be contemptuous. London's only dedicated newspaper remains incredibly loyal to him. Former mayor Ken Livingstone was famously tightly scrutinised by the Evening Standard. However, Channel Four's intensive investigation into Boris's relationship with ABP last week merited a grand total of three paragraphs in the following edition of the paper. Historians will note that Johnson recently returned from his third holiday at the Italian castle of Standard owner Evgeny Lebedev.

In unrelated news, Boris recently returned from his third free holiday with Evgeney Lebedev in his Italian castle. pic.twitter.com/irzQ2WfqQH — Adam Bienkov (@AdamBienkov) November 14, 2014

But this is just one newspaper in just one city. If Johnson does ever stand for a national role, he will face much closer scrutiny from the press and other politicians. If and when that does happen, such behaviour as he exhibited at City Hall yesterday will not be so easily missed.