Former Mayor of London and key figurehead of the “Leave” campaign Boris Johnson (left) and Managing Director of Reid Steel Simon Boyd at a “Leave” campaign event in Christchurch, Dorset ©Ben Birchall/PA Wire/Press Association Images

Read more: Can Sadiq Khan keep London safe?

One clear winner emerged from the May elections. Curiously, the media managed to ignore the victory. In stark contrast to the aftermath of last year’s general election, when everyone attacked the performance of the opinion polls, I can find no journalist or politician this time praising the pollsters for getting London, Scotland and Wales right.

This does not mean that they achieved perfection. But, if the polls were judged like films or TV shows, they would deserve four stars out of five.

They all predicted Sadiq Khan’s comfortable victory in London. Four out of five polling companies were within one point of his final vote share of 57 per cent.

They all predicted that the Scottish National Party would slip back from its vote in last year’s general election, but still come out well ahead of its rivals. Three of the five polls showed the Conservatives overtaking Labour to become the official opposition at Holyrood.

YouGov, the only company to poll regularly in Wales, rightly predicted a slight fall in Labour’s vote, and Ukip’s breakthrough in the Welsh Assembly.

Now to the remaining doubts. The polls, especially those conducted online, still tend to understate Conservative support and overstate either Labour or Ukip support. In Scotland’s regional vote (the one that determined how many seats each party would win), the polls put the Tories on 18 to 20 per cent; they won 23 per cent. In the first round of London’s mayoral vote, four of the five polls overstated Khan’s round-one lead over Zac Goldsmith. In London and Wales, polls overstated Ukip five times out of six.

In short, the defects identified a year ago seem not to have been eliminated. This holds lessons for the coming referendum. I believe the recent performance of the polls casts light on one of the mysteries of recent months: the discrepancy between online and telephone surveys about UK membership of the European Union. If we take monthly averages—and so iron out random fluctuations in individual polls—then online surveys have put the race neck-and-neck in every month this year. In contrast, each month’s telephone polls have shown a clear lead for staying in the EU.

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