How political polling shapes public opinion

The Conservatives won in 1992 despite the majority of polls predicting otherwise

The role and influence of opinion polls have certainly grown since polling began in the UK in 1938.

Labour's Nye Bevan complained subsequently that opinion polls "took the poetry out of politics".

As if to prove his point, polls today both reflect public opinion and are used to test policies and messages that help political parties shape that very same public opinion.

The way polls are conducted has changed enormously over the past seven decades.

At the outset interviews were conducted face-to-face either in the respondent's home or on the street.

By the 1980s, telephone interviewing began to dominate the scene and subsequently we have seen the growth of polling conducted among panels of internet users.

Over the years there have been a few proverbial car crashes: at the 1992 general election, 38 of the 50 polls published during the campaign suggested Labour was narrowly ahead - when the result was a resounding seven-point Conservative lead.

More recently, in the 2014 Scottish independence referendum, one poll by YouGov created a massive stir when it published a 2% lead for "Yes" and the actual outcome was an 11% lead for "No".

Profusion of polls

However, the experience of polling in the 2014 Scottish referendum illustrates how easily polls themselves can become part of the political story.

In recent months my email box has been filled with messages from the Green Party, recording every occasion when its rating in an individual poll matched or surpassed support for the Liberal Democrats.

The Greens used these polls very effectively in their successful campaign to be included in the planned televised debates for the 2015 election.

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Lord Ashcroft's enormous investment in individual 1,000-strong polls in marginal constituencies (by my guess, he must have spent the best part of £1m so far) is another example of polls helping to shape a campaign.

UKIP received 3.2% of the national vote in 2010.

We know it is performing well above its support now but national polls with just 1,000 samples cannot tell us anything about UKIP prospects in specific constituencies.

The Ashcroft polls give us that granular detail and help define the different battlegrounds where the 2015 election will be decided.

Immigration issues

Lord Ashcroft's first tranche of polls in Scottish constituencies gave detailed information about the extent of the rise in SNP support that Scotland-wide polls suggested.

However, these seats were mostly drawn from areas with the largest Labour "Yes" referendum vote and we have yet to discover if a similar picture exists in Labour constituencies where support for independence was less strong.

The great profusion of polls published these days can seem very daunting.

However, what they offer is a great wealth of detail beyond the headline figures that most journalists use.

Do you want to know why the Conservatives appear to be receiving little, if any, reward for national economic recovery?

Go to the October 2014 Populus poll where only 14% of respondents agreed that there was economic recovery in their area and they were sharing in it.

The use of polls to tell the story of a general election has soared since 1970

The polls tell us that immigration is an important issue for the public. Dig a little deeper and they will also tell you that many people have no confidence that any of the main Westminster parties can solve this issue to their satisfaction.

Polling also shows us the changing priorities of the electorate.

The monthly Ipsos MORI Issues Index, unlike most other polls, does not offer respondents a shopping list of issues to choose from but asks for spontaneous choices.

Rejecting Westminster

In recent months it has reflected concerns about issues that mirror responses in other polls; the NHS, the economy and immigration.

However, the January 2015 index had spontaneous mentions of "poverty/inequality" in fifth place, ahead of education and crime.

The MORI series has also seen rises in concerns about low wages and housing since the 2010 general election.

But do such polls influence the political parties?

Of course they do; it would be a rather spectacular form of insanity for parties seeking millions of votes at an election to ignore the views of those people as expressed in the polls.

"White Van Man" was a stereotype coined by the media to describe a certain type of voter

And the line between polls simply registering how policy is being received and polls playing an important part in how policy is actually formed was crossed many years ago.

Past election campaigns that have been framed by appeals to "White Van Man" or to "Worcester Woman" were the result of polls identifying key groups in the electorate that could swing the result one way or the other; and the polling would not just identify a demographic group but also test to death what floats their boat.

With more and more pollsters on the pitch, the six-week-long 2015 election campaign is likely to be swamped with opinion polls.

If 2010 is any guide, many of them will focus on expectations about and reactions to the televised leaders' debates.

But one of their biggest challenges will be to provide us with insights into the unprecedented number of people who currently seem set on rejecting the main Westminster parties on 7 May.

This is likely to be an angry election, and we will be looking to the polls to help us understand what provokes that anger.

I suspect the answer will not be found in headline voting intention figures or in particular policies.

The Ashcroft polls have shown that UKIP's attraction is not based on policy but on attitude, which is why the other political parties have found trying to combat UKIP so difficult: it is like wrestling with eels.

But we need answers from the pollsters - and nobody said this election was going to be easy.