Hindsight, they say, is the only precise science known to man. So, was Mossad’s former head of economic warfare right when he told me that October 7 could have been avoided had Benjamin Netanyahu listened to him and his colleagues in the economic warfare unit he led?

Udi Levy said there’s a “very good chance” that Hamas wouldn’t have grown into “the monster that we faced on October 7” had Netanyahu greenlit his recommendation a decade ago that “Task Force Harpoon” deploy its “financial tools” to choke off Hamas’s illicit funding sources, reversing the relentless growth of its war machine.

It’s a compelling case, as I revealed this week in my BBC Panorama programme Hamas’s Secret Financial Empire. The estimated cost over two decades of building Hamas’s 350-mile “metro” of tunnels was $2.5 billion. Hamas has also grown from a loosely-formed militia to a 25,000-strong force structured along conventional military lines of battalions and brigades armed with laser-guided anti-tank missiles and rocket-guidance systems. Where has all that money come from?

Eulogies to Iran for its generosity from both Hamas and Palestine Islamic Jihad is one answer. “Our complete gratitude is extended to the Islamic Republic of Iran,” said the October 7 mastermind Yahya Sinwar in 2021. A grateful PIJ leader Ziyad Nakhalah has valued Iran’s generosity at “billions”.

But little, if any, of that Iranian largesse has been directed at Gaza’s poor and disposed, said Levy. “Iran never gave one shekel for the humanitarian cause,” he says. “They didn’t care about the Palestinians.” Hamas, though, was benefiting from a multitude of other sources. After it kicked its Fatah rivals out of Gaza in 2007, it imposed a series of high taxes worth about $350 million a year: on companies operating in Gaza, registration of vehicles, licences, birth certificates, and commodities smuggled in to beat the Israeli and Egyptian blockade against dual-use materials.

Hamas insisted to me it has always used its own sources of funds and materials to build the tunnels and fund weapons and salaries for its fighters. But money is fungible, and anything spent on everyday government like health and schools would have freed up money to be set aside for Hamas’s military wing. Annual grants from the Palestine Authority vary but in 2017 it committed to spend $1.7bn on Gaza; since 2017 Unwra accounts show a further annual average of $1bn. Many more millions came from NGOs and charities, both secular and Islamic, from around the world.

Then there’s the oil-rich Gulf state of Qatar, for long champion of the Palestinian cause with close links to Hamas. Since 2012, an estimated $2.5bn has been donated, with Benjamin Netanyahu’s permission, to fund fuel, Gaza’s poorest citizens and civil servants’ salaries. But “nobody really (was) monitoring” the distribution of this aid, says Levy.

Qatar, he says, has also covertly sent hundreds more millions to support Hamas via a state-owned charity and a bank, now the subject of US civil proceedings for allegedly using American banks to funnel dollars to Hamas and PIJ “under the false guise of charitable donations”. Qatar categorically denies that it sponsors terrorist funding.

And then there’s an investment portfolio of holdings in some 40 companies trading across the Middle East and managed out of Turkey. The US Treasury estimates its value at “over $500 million”. Both Israeli intelligence and the Americans allege that the holdings are directly or indirectly owned or controlled by Hamas. The portfolio is an ideal source of ready cash from dividends or asset sales.

I acquired these portfolio spreadsheets at the start of 2020. The Mossad had known about them since 2014 but, with one exception, it wasn’t until 2022 that sanctions began to be imposed on companies in it. It was also clear that acute financial acumen lay behind the management of Hamas’s finances. Its managers could “walk out of the job they do for a terrorist organisation into a FTSE 1000 company leadership” says Tom Keating, director of the Centre for Financial Crime and Security Studies at the Royal United Services Institute.

Levy says Mossad thought it was “a huge strategic mistake” not to authorise Harpoon to target Hamas’s funding. But Netanyahu appears to have believed that Hamas could be contained in perpetuity. He was more concerned with destroying any prospect of a Palestinian state by maintaining the separation of the PA in the West Bank from Hamas in Gaza. As he admitted to his Likud party in 2019, the way to do this was to “support the delivery of funds to Gaza” strengthening Hamas and weakening Fatah. Maintaining this separation gave credence to his mantra that Israel had no credible Palestinian peace partner.

With Netanyahu’s political life now hanging by a thread, like Udi Levy he must be wishing he could turn the clock back too.