…is to ask people who are on the electoral roll how they intend to vote.

That might be obvious to seasoned activists, whose knuckles are skinned from all that door knocking by this stage in the campaign.

Not so to Tessa Jowell, whose confidence that Labour will hold Islington South and Hampstead & Kilburn seems to be misplaced.

Dave Hill’s excellent London Blog for the Guardian asked yesterday: Lib Dem surge in London: do the polls lie?

Yesterday late-afternoon I spoke to Tessa Jowell. She said that many of those telling canvassers they were thinking of voting Lib Dem were young, not sure they would vote at all and possibly not registered anyway. On the strength of this she insisted that Glenda Jackson and Emily Thornberry would hold on to their seats, helped by their local reputations: Jackson’s for rebelliousness, Thornberry’s for grassroots graft.

I’d have thought that a former MP would have known better, but Labour activists, I’ll give you this for free:

Kissing babies is not canvassing. Talking to young people is admirable, non-voters too. They may be future supporters.

But don’t base your forecast for next week’s election on people who won’t be voting.