* So what is meant by corruption?

Robert Barrington, Executive Director of Transparency International UK

That is a question that is difficult to answer of any country. Most means of measurement are imperfect; corruption is by its nature a hidden activity; and at times the victims are unaware, or do not know the cause, of their suffering and injustice. At TI, we tend to try not to accuse entire countries of being corrupt or not corrupt, as we do not believe that the citizens of any country are innately corrupt.

But it is very evident that corruption in certain forms is more prevalent in some countries than others.

So what is meant by corruption? Of course, it comes in many guises, some illegal, and some legal. TI-UK was clear that the MPs expenses scandal was an example of corruption, at the very heart of Parliament - and yet few MPs were prosecuted, and even today, many MPs will write it off as an irritation in which they were badly misunderstood and got at by the media.

Likewise, we feel that the UK's environment for lobbying, the revolving door and political party funding opens the door to corruption, even though much of it is so hidden it is known about only through rumour and sting operations. Our report last month Lifting the Lid on Lobbying found 39 loopholes in the system - and shortly after its publication, we had the Straw and Rifkind affair.

As I wrote earlier this week about the police, the Cyril Smith case highlights that although the UK performs well on most standard corruption measures, there is a lingering feeling that beneath the surface there is an underlying corruption of cronyism and impunity that somehow feels uniquely British. Invisible, deniable, insidious, difficult to legislate against, sometimes appearing to do little harm except inexorably tilting the system in favour of its beneficiaries, sometimes doing great harm.

And one aspect of corruption that is not captured by any reliable quantitative data is the UK's role as a facilitator of global corruption through providing a safe haven for corrupt capital - the subject of our recent reports Corruption on Your Doorstep and Closing Down the Safe Havens. As with Parliament, we found both that there is illegal behaviour, but also that much behaviour that facilitates flows of corrupt capital is entirely legal.

Good definitions of corruption are difficult to find - of course, TI has one of its own, and of course, some people prefer other definitions. On the one hand, it's important not to draw a definition too narrowly. On the other hand, although tempting, you can easily end up with a definition so broad that it encompasses all injustice, all inequality and all failures in ethics or integrity. Whatever the definition, I think some key ingredients are that it encompasses both legal and illegal behaviour; the public and private sectors; visible forms such as bribery and less visible forms such as cronyism.

I read a piece in the Guardian this week by George Monbiot, reviewing a new book called 'How Corrupt is Britain?'. The book is published this week, so I've not yet had the pleasure of reading it, but I am delighted that more academics are taking this subject seriously. One of the conclusions of our own 2011 study on Corruption in the UK was that there is simply not enough research on the subject. Our report stated: 'The research suggests that we do not understand the full extent of corruption in the UK and that we need a more coherent and joined up approach to tackling the problem.

There is complacency and a lack of knowledge of the extent of corruption in key sectors and institutions. The policy response is incoherent and uncoordinated. This inadequate response has in certain areas created a culture of impunity.'

One of George Monbiot's comments is that TI's Corruption Perceptions Index (CPI), which ranks the UK as 14th in the world, is the wrong way of measuring corruption in the UK. His view is entirely in line with TI's own view that the CPI measures certain things about corruption, but not others.

I always urge policy makers to look in much greater depth than a single index, particularly at TI's Global Corruption Barometer - which, for example, found in 2013 that 69% of people in the UK felt that the media were corrupt or extremely corrupt, and that 60% felt that the government was entirely or to a large extent run by a few big interests looking out for themselves.

I recently spoke to an American academic who told me that the thing he least liked about TI is the Corruption Perceptions Index; but the thing he most liked about TI was that it had responded to criticisms of the CPI by creating a family of indices and body of research that give a much fuller picture. That's encouraging - but it is also the case that every corruption index produced by TI or others has its own body of critics - academics who don't like the methodology, activists (including those within TI) who don't feel it shows a full picture, governments or companies that don't like the results, and so on.

One of the most convincing summaries of UK corruption I have come cross is UK Anti-Corruption Scorecard we published in 2013. It rated the UK using a traffic light system on 26 indicators - and the score was 6 red, 14 amber and 6 green - with many of the green relating to the UK's actions in the international arena, and not within the UK.

So how corrupt is the UK? An optimist would point out that it is not Russia or Afghanistan. And for most people it is not: the daily lives of citizens are less blighted by corruption than in either of those two countries. Optimists would also point to the new UK Anti-Corruption Plan as a sign that at last the UK government is starting to wake up to the threat posed by corruption. For the record, TI-UK gave the plan a qualified welcome - a good plan but with political will yet to be proven. But a pessimist would say - hold on. The hidden corruption in the UK, permitted by laws that have been passed by a corrupt elite of business people and politicians, and its complicity in global flows of corrupt capital, make a mockery of indices that just measure people's experiences and perceptions.

Inevitably, both views are right. By most objective analysis, corruption is not as bad in the UK as in some parts of the world; but it is much more profound in the UK than many people understand or admit. Perhaps the biggest danger for the UK is complacency.