For the past few years, Boris has looked like a likely two-term Mayor of London. He has surprised many skeptics with his seriousness of purpose even while amusing and thoroughly charming them. Now two polls (from YouGov on Friday and ComRes yesterday) show Ken sneaking a 2% lead to win the showdown on May 3rd.

Ken’s numbers have improved even as Labour’s numbers nationally have worsened, but nevertheless Ken is still polling far below his party: Labour maintains a huge lead in London, but Ken is only a nose in front. It shows what a strong performer Boris is that he remains a contender. People do like Boris – even when he talks purposefully about buses his listeners tend to smile with pleasure. His competence is no longer in doubt, he works hard and he has a string of acknowledged achievements. But will all that be enough to stop Ken providing Labour with a much-needed dose of momentum? This really matters to Cameron: whenever we have seen a change in the government of Britain, it has been preceded by a change in London.

The recent slide comes largely from Labour supporters becoming more loyal to their own: 23% of Labour voters had previously opted for the energetic Boris, now it’s only 12%. The follow-up questions in our poll show things nicely balanced for an intriguing campaign: Boris wins strongly on ‘charisma’, while Ken wins big on being ‘in touch’. Boris is ahead on crime, Ken is ahead on transport.

So what does Boris need to do to ensure victory? Last week he spent a big chunk of political capital fighting for a new airport in the Thames Estuary. But voters don’t care about that. The danger for Boris is that they may enjoy Boris rather more than they truly value his strengths. Our poll showed the least important issues to Londoners were ‘Promoting London’s image’ and ‘Promoting the Olympics’, things which Boris most likes to do.

What London voters really care about is crime, transport, and cutting the high cost of living in the city. Crime is already a plus for Boris; now he needs to concentrate on winning the argument on transport. And he can best show he cares about easing the financial burden on Londoners by lowering its price.

One way is to take his recent hint of a driverless tube and upgrade it into a firm battle-cry policy. It would allow him to dangle the prospect both of higher-quality transport and lower fares. The DLR is already driverless, and it’s a great service. The Victoria Line is fully automated and the ‘drivers’ are unnecessary, a mere totem of an earlier era. The rest of the world has long embraced this obvious modernisation. Plans to make the whole tube driverless have indeed been well developed but are gathering dust.

Making those plans into reality would save money and improve reliability. Of course, it would also lead to long and painful strikes. If Boris were to announce before the election this firm, timetabled intention to transform the tube service, he would have a major controversy on his hands – it would no doubt become the main campaign issue and it could backfire. The unions may even call a strike in advance of the election, as a warning shot. But I suspect this would more likely gain Boris votes (as Ken would surely support the unions). Were Boris then to win the election, thereby getting Londoners’ clear endorsement for his policy, it would be much harder for the unions to defeat progress towards an efficient and strike-free transport system. And Boris would go down in history as one of the great Londoners.