Probably based on the ’wheel-turning monarch”.
But the system such a monarch would implement would be nothing like the type of monarchy we know of.
‘But sire, what is the noble duty of a wheel-turning monarch?’
‘Well then, my dear, relying only on principle—honoring, respecting, and venerating principle, having principle (Dhamma) as your flag, banner, and authority—provide just protection and security for your court, troops, aristocrats, vassals, brahmins and householders, people of town and country, ascetics and brahmins, beasts and birds.
Do not let injustice prevail in the realm.
Provide money to the penniless in the realm.
DN 26
I mean child labour for children under age 6 years was only banned 1835 in great britain.
For children under 14 years only much later in 1933…
Also british prisons initially put men and women, girls and boys (children) all in the same prison(!)
Then there was of course also british colonialism, which is pretty much fascism but instead done abroad.
And a whole lot more of inhumane things…
So if one imagines the Buddha supported something so degenerate as british monarchy (or any other types of ruthless monarchs), one is really changing the narrative.
Rather in the case of the wheel-turning monarch it is a rule of true peace, human rights and animal rights, education (dhamma) and no poverty. 
The Buddha himself is the wheel-turning monarch if he chooses to neglect the spiritual path.
So a Buddha/Wheel-Turning Monarch being born in the world is a win-win situation regardless which path he may choose. 
The Buddha, as we all know, also rejected the caste system in numerous suttas and in many different ways, that any class of people is somehow superior to another class.
But please keep in mind that during the Buddha’s time caste was not really enforced that much in India compared to when the british arrived and made it into laws….
He clearly rejected greed as in exploiting people/workers or overindulging in luxury items and food and so on.
He clearly rejected hatred as in blaming problems on and then demonizing and lying about other people to the point of hatred, persecution & violence.
He clearly rejected the delusion that birth in a certain family alone makes one a noble person. And rejected all the delusions regarding fame and wealth etc.
”Let them enjoy the filthy, lazy pleasure of possessions, honor, and popularity.” 
So it ought to be quite clear that the Buddha did not see monarchy as the ideal system of rule at all.
Rather he would start his journey as a wheel-turning monarch but the system finally implemented as monarch would mostly have only leftist ideas. 