After an eight-year detour into municipal government, Boris Johnson has now returned to national politics. The former mayor of London will mark this moment by going on the stump for the Leave campaign. He has some catching up to do: while never far from the public eye, he was absent from the Commons for seven years. Even when back in Parliament after the general election, Boris felt he could not take the cabinet job that was offered to him.

But his time at City Hall hasn’t dented his ambitions; quite the opposite. He is the bookies’ favourite to be the next Prime Minister. Indeed, he returns to the national scene in a far stronger position. In the summer of 2007 when he announced his intention to run for mayor, his political career had stalled. He was Tory spokesman for higher education but not a full shadow cabinet member. Although he had backed David Cameron for the leadership, it was clear Cameron was never going to give him a big job. What’s more, his Commons performances had been disappointing. A style of speaking that worked so brilliantly outside the chamber didn’t work inside. Mr Cameron would privately remark that his fellow Old Etonian was ‘stuck in a buffoonish rut’, unable to make the transition from entertainer to politician.

Eight years of running London, after two Tory victories in a Labour city, has changed all that. Boris is now a serious contender for the leadership in a way he simply wasn’t in 2007, and wouldn’t have been had he stayed in the Commons. He could be the first Prime Minister since the Duke of Wellington to enter No. 10 because of what he did outside Parliament. Rather than make it to the front bench then climb the greasy pole, he has blazed a new career trail for the ambitious.

One can argue that he is sui generis. Yet, devolution should produce more Borises. It should be entirely possible for a politician to make his or her name running a city and then arrive at Westminster as a plausible potential Prime Minister. The new mayor of Greater Manchester will be in charge of a £7 billion budget, larger than that of several government departments.

If Boris is not simply a one-off, but the first of a succession of former mayors to enter Parliament with high ambitions, it could improve the quality of governance in Britain. One of the flaws of our system is that the executive is led by members of the legislature — so we often end up with new ministers who haven’t run anything more taxing than a tombola stall. Mayors, by contrast, will come to Parliament already blooded in the arts of winning elections, fighting bureaucracy and delivering public services.

But devolution is a mixed blessing. When New Labour created the Scottish parliament and the Welsh assembly, the expectation was that ambitious young bucks would cut their teeth there then graduate to Westminster. Instead, the assemblies ended up stuffed with those who aren’t, or weren’t, good enough for Westminster. Remarkably, even the Scottish National Party seems to have sent its best talent to London. Joanna Cherry, the highly impressive QC who speaks for the SNP on justice and home affairs at Westminster, would surely be a more effective Scottish justice minister than the incumbent, Michael Matheson, who was a community occupational therapist before he went to Holyrood.

Some Tories hope that their leader in Scotland, Ruth Davidson, can be persuaded to make the journey south. If elected as an MP, they argue, she would immediately be a leadership contender because her ‘proper, old-fashioned blue-collar Toryism’ is what the party needs. They believe she is the party’s most naturally talented politician.

Davidson is fond of saying she has no Westminster ambitions. But she certainly has options. She grew up in the Borders, one of few parts of Scotland where Tories stand a chance of being elected to Westminster. Whether her style of politics would work there is another matter. When Boris Johnson was on TV explaining his decision to back Britain leaving the EU, Davidson sarcastically tweeted: ‘Is it just me or is Boris floundering here? Not sure the bumble-bluster, kitten smirk, tangent-bombast routine is cutting through.’ One of her allies admits: ‘She is a bit too free-and-easy about making it known what she thinks of people. If she wants to come down here, she is going to have to be a bit more careful about that.’

The viciousness of Davidson’s comments indicate a problem for Boris. ‘He has people who will do absolutely anything to stop him,’ one cabinet minister tells me. Some loathed him even before he came out for Brexit; others were enraged by that decision. And his enemies are delighted that he has not had the easiest of starts to his referendum campaign. Michael Gove is now the hero of the Brexit-backing grassroots, they declare. And a survey of party members by the Conservative Home website showed Gove top, and Boris in fourth place.

But Boris does tend to start slowly on -campaigns; it takes time before he gets into his stride. He is about to embark on six weeks of intensive Brexit stumping and come polling day on 23 June he should be in fine voice. Downing Street’s reluctance to put forward anyone in government to take him on in the TV debates suggests they have more respect for Boris and his argument than they care to admit.