If you think you're middle class, you're almost certainly upper middle class.

Seventy per cent of the Scottish population lives on less than the average wage of £24,450. If any of you are earning 30-something salaries you probably think you're sort of "normal". Actually, that puts you in the wealthiest 15% of Scots. Above that, you're the elite.

All parliamentarians and senior civil servants are in the top 5% by income. They invite people to "bring them information" about the world outside through public bodies, evidence sessions and inquiries. It turns out that overwhelmingly they seek advice from people on the same income as them.

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Meanwhile, the rest of the population – the 70% – make up only about 3% of the people giving that advice. If we had accurate data (virtually none is collected) the picture would almost certainly be much, much worse.

Does this matter? Isn't the best available expertise what we should be looking for? Not if we are conflating "expertise" with "vested interests". Who has the real expertise on poverty, on patient care, on health and safety? It certainly isn't the director of the CBI.

We think we know how other people live, but we don't. The world looks different when the monthly margin of error in your family budget is £10 rather than £200, when you don't "support" public services but need them.

For many years I had a well-paid career influencing policy. On a top-10% salary I listened to discussions in which promoting private profit, keeping tax on the wealthy low, privatising public assets and rolling back public services were assumed to be the unchallenged goals of government.

Back home with my friends in the other 90%, nothing could have been further from their concerns; economic security, good public services, enjoying their job.

In our report, a psychologist explains that leadership divorced from those being lead is prone to bias and results in poorer decision-making.

This is not about individuals. It is about diversity, difference of opinion, different perspectives and values. It is about representation.

So what do you do when those who ought to be fixing a problem are the problem? Look elsewhere for the answers. We are launching a Joseph Rowntree-funded commission to ask for ideas from groups and individuals who are not "insiders".

What answers might there be? How about citizens' juries. In Scotland, 15 randomly selected members of the public are trusted (with guidance and support) to make decisions about guilt or innocence in complex criminal trials.

Imagine if we had taken the same approach to the inquiries into the Iraq War, the financial crisis or media corruption. It is hard to imagine a citizens' jury being so quick with its exonerations or so confident that inaction is the best way forward. They have been shown to be highly effective even in making complex policy decisions.

Another response would be a binding charter on committees and inquiries that requires them to take evidence in proportion to those affected. Allowing a group of finance directors to explain why public services "must" be cut without listening to the communities affected by those cuts is bound to produce a unbalanced picture. The same goes for making controversial decisions on the basis of lobbying from half a dozen well-funded employer organisations but only one token contribution from a representative of employees.

We are very interested to see what other ideas come in – tried and tested practice or completely new approaches. But whatever, there is one thing that we must do if we are to take this seriously. We need to start collecting data.

We now accept that monitoring equal opportunities is important to make sure we are not excluding large sections of society on grounds of gender or ethnicity.

We need to do the same with wealth. We need an audit of the socioeconomic position of our political insiders so we have a proper picture of how social class and political priorities interact. Excluding 70% of citizens from running society is not sustainable. It is time to make government of the people by the people for the people mean something again.