Fortunately, like every other candidate in this campaign, Mr Linton has a helper with a mobile phone. He can be tracked down to the Duke of Devonshire pub, grabbing a late lunch, before proceeding to “blitz” a few Labour streets at the southern end of the constituency, where it borders Tooting and Balham.

“Blitzing” means door-to-door canvassing in areas where there is known to be a high degree of Labour support but where voters are reluctant to turn out. Every vote will count in this Tory-held marginal, where Conservative MP John Bowis is defending a majority of less than 5,000. Labour is only canvassing known Labour supporters and those whose intentions are unknown, and all are offered the opportunity to meet the candidate.

So what do they say when they do? Is it true, as a recent London Evening Standard MORI poll found, that education is top of the voters’ concerns in London, ahead even of health and law and order? Battersea, in the Tory flagship borough of Wandsworth, where selection, opting-out and nursery vouchers are all on the menu, should surely be a constituency where voters want to talk about schools.

Mr Linton considers. He reckons that education is probably the subject raised with him most often after health. But he points out that the proportion of voters with school-age children is quite small and that the number affected by, say, the competitive scramble of finding a secondary place in the borough, is even smaller. Children often travel a long way to secondary school these days anyway, he says: his own daughters went to a comprehensive in Richmond.

At the front door, voters often want to talk about very little. There is the elderly lady who, when asked about her voting intentions, replies: “That’s for me to know and you to find out.” (Mr Linton, commendably, does not bite her ankles. )

In these Labour streets, most are friendly and say they will vote Labour, including two who appear to be “switchers” from the Tories. But in three streets only two voters raise the subject of education. The first praises her child’s primary school in Labour-run Lambeth; the other, worried by asthmatic children drinking cold water in our cold winters, thinks schools should allow pupils hot drinks at lunchtime.

“Class size is a very good issue for us,” says Mr Linton, referring to Labour’s pledge to use money saved from ending the Assisted Places Scheme to cut all infant classes to no more than 30. He points out that Wandsworth’s good average class size conceals great variations and that the borough’s total of 2,300 children in classes over 30 is the highest in inner London.

What about the abolition of the Assisted Places Scheme? Emanuel School in the constituency has more than 300 pupils on assisted places. “It has been raised once or twice,” says Mr Linton, “but I say it’s immoral to spend taxpayers’ money on a small proportion of the electorate - it should be for all. They usually find it hard to defend.”

Things do not appear in quite the same light to John Bowis, found with his helpers in the Falcon pub near Clapham Junction consuming an enormous Cumberland sausage. One Tory voter told Mr Bowis: “I’ve got three children on assisted places: how else can I vote?”

Mr Bowis, transport minister for London, is bullish about his prospects. “It’s most encouraging,” he says, claiming to have found hardly any “switchers”. He appears to see no sign of the massive London swing to Labour found in the Evening Standard’s MORI poll, giving Labour a 32 per cent lead over the Tories. If proved correct, 32 Tory MPs would lose their seats in London, including Mr Bowis.

He lists education as one of the most frequently raised issues, along with Europe, crime and tax. Doorstep worries include discipline and the quality of teaching. There is also resentment about children from neighbouring boroughs swelling the classes in Wandsworth primary schools - the real reason, say the Tories, for the oversized classes in the south of the borough.

One of Mr Bowis’s helpers likes to point out the difference between Tory-run Wandsworth, where parents are queuing up to get their children in,and Labour-run Islington, where you-know-who can’t wait to get his children out.

As for the borough’s secondary schools, Mr Bowis says he has heard complaints about parents not getting their children into their chosen school but none about the tests children have to sit.

He cites a Tory waverer the previous evening complaining that, after 18 years of Conservative government, there was still no grammar school in Wandsworth.