Demure, veiled and black-clad women slip quietly to the toilet as an aircraft leaves Saudi Arabian airspace. They return to their seats in glamorous haute couture dresses and expensive jewellery.

It's a paradox that sums up one of the many challenges facing 32-year-old Mohammed bin Salman, Saudi Crown Prince and heir apparent to ailing King Salman.

After a meteoric rise to power in the kingdom whose hallmark was consensual change at a glacial pace he has, with almost Donald Trump impetuosity though hopefully with far greater strategic thought, started overturning the old order.

The veiled women on the plane will in June be allowed to drive for the first time. They will be allowed to go to the cinema, the first time for 35 years movie theatres have been allowed, and sit in mixed, rather than the currently segregated, audiences.

Agenda: Iran's brutal and corrupt regime must be brought down

The kingdom has promised for the first time to issue tourist visas in the first quarter this year.

But Prince Mohammed walks a tightrope as he modernises the socially conservative kingdom and reduces its formerly total dependence on oil revenue amid historically low crude prices.

He must carry with him the austere Wahhabi religious establishment the Al-Sauds have depended on since the kingdom was founded in 1932 as he promotes “moderate Islam”. His surprise move to clip the wings of the religious police who enforce their view of morality surprisingly passed without overt opposition.

His Vision 2030 set out hopes to wean the world’s largest oil exporter away from oil revenue. But how to implement this astonishingly ambitious project, that includes a new $500 billion mega-city powered by renewable energy, looks increasingly doubtful.

Agenda: Iran's brutal and corrupt regime must be brought down

His decision this month to introduce VAT at five per cent in a currently tax-free country and more than double some fuel prices met with protests.

The night of the long knives on November 4 that saw some of the kingdom's most powerful figures arrested and held in a luxury hotel till they repaid allegedly corrupt wealth demonstrated his steely resolve and grab for power.

Saudi youth – about 70 per cent of the population of some 28 million population are under 30 – have warmed to his ambition and pace of change, though the trickle down effect to more jobs remains to emerge. Prince Mohammed’s personally extravagant life style, for example his 500 million Euro yacht and $300 million French chateau, have somewhat dented his image.

It is in the foreign arena, however, that some of the Sunni kingdom's greatest challenges lie. Iran is vying with Sunni Saudi Arabia for regional dominance. Protests across the world's only Shia state this month are unlikely to dent its ambitions despite resentment among demonstrators at the diversion of domestic resource to foreign adventures.

Iran sees its influence through proxies in Iraq and Syria and particularly through Hezbollah, the Lebanese military group that is part of government, giving it growing influence and access all the way to the Mediterranean.

Agenda: Iran's brutal and corrupt regime must be brought down

Saudi efforts to counter the rise of Shia Islam and Tehran have seen few results.

Most spectacularly, and tragically, a Riyadh’s attempt to defeat the Iran-supported Houthi Shia group in Yemen has resulted in mass starvation and the world’s worst humanitarian crisis. Fighting and bombing have claimed some 10,000 lives but peace seems nowhere in sight.

Prince Mohammed’s abrupt severing of relations with neighbouring Qatar, a fellow member of the Gulf Cooperation Council which was founded to provide Sunni solidarity after the Iranian Islamic revolution, has achieved little beyond fracturing unity on the Arabian peninsula.

In Lebanon, his attempt to neuter Iranian-backed Hezbollah seems to have failed. It is widely believed that the recent strained resignation statement on Saudi television of Lebanese prime minister Saad Al-Hariri while on a visit to Riyadh was forced on him. Mr Hariri, under pressure to curb Hezbollah, subsequently withdrew his resignation on return to Lebanon.

Saudi Arabia has become increasingly and publicly closer to Israel, an unexpected turn of events for a former foe because of Riyadh’s support for the Palestinian cause. This may be another attempt to fight Hezbollah which threatens both Riyadh and Tel Aviv.

As 2018 begins, the firebrand prince with the big ambitions must deliver results both at home or abroad or face domestic opposition in his ambitions to be king.

The Shia-Sunni divide in Islam began when the Prophet Mohammed died in 632 and his followers disagreed over his successor.

One group argued it should be kept in the family and backed Ali Ibn Abu Talib who as Mohammed's first cousin and son-in-law was his closest relative. They became the Shi'at 'Ali (Shia) or Party of Ali.

Agenda: Iran's brutal and corrupt regime must be brought down

The majority wanted the most pious Moslem who would follow Mohammed's practices and beliefs, the Sunnah. They chose Abu Bakr and became the Sunnis who now make up about 90 per cent of Moslems.

The Iranian Islamic Revolution in 1979 triggered the current rivalry between the groups after relative calm in relations since the collapse of the Ottoman Empire after the First World War.