A year or so before David Cameron became Prime Minister, there was an awkward moment when he struggled to pinpoint how many properties he owned. ‘Do not make me sound like a prat for not knowing how many houses I’ve got!’ he begged the interviewer. He spent the rest of the conversation fretting about how he would come across.

The PM has always been aware that if voters knew the scale of his wealth, they would consider him incapable of relating to their daily struggles.

Downplaying his family fortune has been vital to his political success – which is why this week’s reminder about his father’s links to tax havens is so potentially toxic.

David Cameron has always been aware that if voters knew the scale of his wealth, they would consider him incapable of relating to their daily struggles

Downplaying his family fortune has been vital to his political success – which is why this week’s reminder about his father’s links to tax havens is so potentially toxic. He is pictured with his father Ian in 2010

To Westminster watchers, the revelations about the late Ian Cameron’s tax-avoidance schemes may sound familiar. It has long been known that he made a very comfortable living advising wealthy clients how to avoid contributing to the public coffers.

In any case, the prime minister cannot be held responsible for his late father’s financial decisions.

Cameron senior launched his business way back in 1979, when such markets were only just being opened up to British investors. There was none of the political sensitivity surrounding such arrangements that there is today.

Cameron’s problem is the lingering suspicion that he himself benefits from offshore funds in some way, an impression he has failed to dispel by dodging the question this week. Although, it has to be said, he has admirably done more than most world leaders to call for a crackdown on tax-avoidance.

It is just bad luck that some of his relatives have assets owned in offshore companies or work for firms based in tax havens. It means he is deeply conflicted on an issue he himself has chosen to make a very public political priority.

Over the years, he has gone to great lengths to create the illusion that he is only a bit better off than most. During the Easter holidays, for example, he made a point of taking a bargain basement Easyjet flight to Lanzarote, a popular and relatively affordable holiday destination.

His mother Mary is descended from a wealthy MP who owned a grand house in Berkshire on a 660-acre estate

When Samantha’s parents divorced, her mother Annabel, who runs the furniture and interior retailer Oka, married another wealthy aristocrat, William Astor. He owns an 18,736-acre estate on the remote Scottish island of Jura (pictured) which David Cameron adores

Not for him the style of break favoured by Tony and Cherie Blair, in luxury private yachts and Tuscan villas borrowed from princes and billionaires. Indeed, he and Samantha seem genuinely content to holiday in Cornwall, Portugal and Ibiza (the latter a particular favourite with Samantha, who loves the searing summer heat and music scene).

To emphasise the point, Cameron’s children attend state schools (for the time being at least). Even the family home in Witney looks quite ordinary from the road. (It helps that you can only see a fraction of the property, which is substantial, but tucked behind another house.)

The truth is, however, that by almost any standards, the couple are stupendously rich.

As Cameron himself once jokingly put it in private, he was ‘born with two silver spoons’ in his mouth.

When Samantha’s parents divorced, her mother Annabel, who runs the furniture and interior retailer Oka, married another wealthy aristocrat, William Astor

The money is inherited as well as self-made. Both the PM’s parents were well off. His mother Mary is descended from a wealthy MP who owned a grand house in Berkshire on a 660-acre estate. His father Ian came from a long line of successful bankers and financiers (Cameron’s paternal grandfather Donald left the equivalent of nearly £1m in his will in 1958, a huge sum in those days.) Ian, who worked very hard, set up his own business shortly after it became legal to shelter money overseas to avoid UK tax.

He proved very skilled at the work – so much so that in 2007 the Sunday Times Rich List estimated his wealth at £10million.

In the 1970s and 1980s, his expertise in tax avoidance funded a very comfortable lifestyle for his young family, enabling him to send all four of his children to private schools and have wonderful holidays.

As a result of this lifestyle, Cameron was an extremely sophisticated teenager. (His godfather Ben Glazebrook remembers him nonchalantly recommending a gourmet French dish from a Soho restaurant – at the age of 14.) Four years before Ian died in 2010, the Prime Minister’s older brother, Alex, became sole owner of the Rectory where they all grew up – a move likely to have significant implications for reducing inheritance tax liabilities on the property.

According to reports, around the same time, another family property in Kensington, worth £1million, passed to Cameron’s two sisters, Tania and Clare, in equal share.

When Ian died, suddenly on holiday in France, his estate was valued at just £2.74million. Crucially, however, his will only detailed his UK assets. In April 2015, a Channel 4 investigation confirmed what many had long suspected: that he had left money squirrelled away in Jersey. Quite how much is unknown, but the ‘grant of probate’ filed in Jersey and attached to his will would only have been required for assets of more than £10,000. Cameron’s father also had financial links to Switzerland – raising the possibility that the family retains assets there.

All this would be enough to put Cameron in a league well above the hard-working middle classes. It is Samantha’s money, however, that pushes the couple into the ranks of the super rich.

She, too, has made an art of underplaying it. In her twenties, she would tell people that her father Reggie was a ‘farmer’. In fact, Sir Reginald Sheffield is the eighth holder of a baronetcy that dates back to 1755, and has a property portfolio worth upwards of £20million. It includes 3,000 acres of arable land; a £5million stately home near York; a place in London; and the family seat in Lincolnshire, a Regency mansion called Normanby Hall.

SAM CAM'S £77,000 STAKE IN FAMILY FIRM Samantha Cameron owns shares in a £2.2million family firm, Downing Street confirmed yesterday. It is run by her father Sir Reginald Sheffield and linked to his estate near Scunthorpe. Downing Street said she declared the shares on her tax return. There is no suggestion the firm is run offshore. But its interest in a proposed 1,000-home greenfield development in Lincolnshire led to criticism in 2013 that Mrs Cameron’s stake was not included in her husband’s list of financial disclosures. Developers used government planning reforms to argue for the scheme, potentially worth £20million. But Cabinet Secretary Sir Jeremy Heywood deemed it not ‘relevant’ to be included in the Prime Minister’s public declaration of interests. Mrs Cameron and younger sister Emily own a small stake in Normanby Estate Holdings, run by their father. The most recent accounts show its assets are worth almost £2.2million, which values Mrs Cameron’s holding at just under £77,000. Mrs Cameron also received an estimated £400,000 windfall from the sale of stationery firm Smythson. She was a creative director for the company and owned a reported 275 shares when it was sold in 2005 to a consortium of City grandees. Advertisement

When Samantha’s parents divorced, her mother Annabel, who runs the furniture and interior retailer Oka, married another wealthy aristocrat, William Astor.

He owns an 18,736-acre estate on the remote Scottish island of Jura, which has been held in an offshore company called Ginge Manor House, based in Nassau. (The company has the same name as Viscount Astor’s home in Oxfordshire.) Cameron adores the tranquillity of the Hebridean estate, and used to holiday there regularly, but the link with the Bahamas has been a periodic embarrassment. In the past, Astor has vigorously defended the (entirely legal) arrangement, which dates back to the late 1960s. He says it has no tax benefit.

As for Samantha herself, she far out-earned her husband as creative director at the luxury leather goods firm Smythson, though in 2010 she scaled back and became a creative consultant at the firm. It, too, is based in a tax haven. It is owned through a holding company in Luxembourg and linked to a trust in the Channel Island of Guernsey, another well-established tax haven.

Then there are the wealthy friends who donated to Cameron’s leadership campaign, two of whom, JCB boss Anthony Bamford and the Fleming family, who made their fortune through investment banking, feature in the so-called Panama Papers. (Bamford has said that the company he held in the British Virgin Islands was never active, nor owned any assets.)

As for Samantha herself, she far out-earned her husband as creative director at the luxury leather goods firm Smythson, though in 2010 she scaled back and became a creative consultant at the firm

To make matters more awkward, Chancellor George Osborne has had his own difficulties with links to tax havens. Last year it emerged that his family’s business, Osborne & Little, made £6million from a property deal with a developer based in a tax haven.

All of which is unhelpful for a prime minister who has made such efforts to try to end ‘tax secrecy,’ labelling some offshore schemes ‘not fair and not right’.

Last night, he continued to insist his family’s tax arrangements were a ‘private matter’. Under pressure to reveal whether he benefits from any investments held in offshore trusts, he has chosen his words very carefully, saying that he does not ‘own’ any shares, offshore trusts or offshore funds, and that neither his wife, nor their children, ‘benefit’ from such arrangements. It stops short of a denial that they stand to benefit from such assets in future.

Of course there is no crime in being wealthy, and all the Camerons have worked very hard to get where they are today. Some of them are also commendably civic-minded.

His mother, Mary, has devoted much of her life to good works. A former part-time magistrate, she is a pillar of the community in her village of Peasemore in Berkshire and is involved with multiple local charities, to which she quietly devotes time and money without seeking any public recognition.

The irony of this week’s revelations is that no recent party leader has done more than Cameron to crack down on tax avoidance, and in contrast to the Blairs, is a model of financial rectitude.

Indeed, Tory loyalists yesterday took to Twitter to claim that he made more than 40 changes to tax law in the last parliament to close loopholes Labour ignored.