Two of Italy's wealthiest regions are seeking greater autonomy in a pair of referendums to be held on Sunday, with Catalonia's secessionist ambitions in Spain looming large over the debate.

While the presidents of Lombardy and Veneto in northern Italy are campaigning on the economic benefits of loosening Rome's grip, identity politics also plays a role - particularly in Veneto, heir to the once-vast Venetian Republic.

There, a political fringe has never given up on secession even though it has been long abandoned by the governing Northern League party.

Both Veneto president Luca Zaia and his Lombard counterpart Roberto Maroni emphasise the legal nature of the referendums, which were approved by Italy's constitutional court.

Veneto president Luca Zaia (right) and his Lombard counterpart Roberto Maroni (left) are holding referendums seeing greater autonomy in Italy on Sunday

A giant poster on Sunday's referendum on whether to demand greater autonomy hangs on side of a building in Milan, Italy

In contrast, the October 1 Catalan independence referendum was declared illegal and vigorously opposed by the central Spanish government in Madrid.

The autonomy drive is a powerful threat to Rome's authority. Together, Veneto and Lombardy account for 30 per cent of Italy's GDP and almost a quarter of the nation's electorate.

Both regions are run by the anti-migrant, anti-Europe Northern League, which has found allies for autonomy in other centre-right parties like former premier Silvio Berlusconi's Forza Italia and the populist 5-Star Movement.

They hope to spread the autonomy model to other Italian regions.

In Veneto, the secessionist fringe appeals to a common identity: a shared Veneto dialect, traditional poor man's fare like polenta, and a self-image of hard-workers whose family-run businesses helped power Italy's post-war economic boom.

There is also the proud history of the Venetian Republic, which for more than 1,000 years dominated a vast territory comprising Veneto, parts of Lombardy and much of the eastern Mediterranean.

One Veneto separatist group, Plebescito.eu, is vowing to resume the independence campaign once Sunday's referendum has been held.

Another party, Veneto Independence, was behind a failed attempt to gain constitutional court approval for a Veneto referendum on independence.

While the presidents of Lombardy and Veneto in northern Italy are campaigning on the economic benefits of loosening Rome's grip, identity politics also plays a role - particularly in Veneto, heir to the once-vast Venetian Republic

Together, Veneto and Lombardy account for 30 per cent of Italy's GDP and almost a quarter of the nation's electorate

Playing on an identity as Italy's underdogs, they note widespread scepticism of the autonomy referendums elsewhere in Italy and among the centre-left, with critics arguing that the non-binding vote carries no legal weight, is not needed to trigger autonomy negotiations and is a costly waste of resources.

For backers of the referendums, such put-downs are part of elite, centrist decision-making in Rome that ignores the periphery - sentiments echoed elsewhere in the Catalonia referendum, in the US election of Donald Trump and in Britain's vote to leave the EU.

The date of the referendum is laden with symbolism: October 22 is the 151st anniversary of the 1866 Veneto Plebiscite, a popular vote that united Veneto with Italy. Modern-day separatists see that vote as invalid, due to low turnout.

Even Mr Zaia's official video poses the question in stark nationalist terms: 'I choose Veneto. I choose liberty.'

The Veneto autonomy drive is strongly motivated by a sense of injustice at having to share tax revenues with Italy's poorer south and envy at the relative prosperity in the neighbouring regions of Trentino-Alto Adige and Friuli-Venezia Giulia, which are among five regions made autonomous under Italy's 1946 constitution in recognition of their unique status.

While Trentino-Alto Adige is largely German-speaking, Friuli-Venezia Giulia was recognised for its position bordering then-Yugoslavia as a Cold War hedge.

Catalonia's secessionist ambitions in Spain are looming large over the debate. Pictured above, pro-independence supporters holding Catalan flags take part in rally near the Parliament, in Barcelona, Spain, on October 10

However, Veneto historian Giuseppe Gullino challenges the notion of Veneto identity, saying attempts to leverage the Venetian republic ignore that much of it lay outside present-day Italy, sweeping into Istria, past the Ionian islands and Crete and all the way to Cyprus.

'There is a pride in the history, which in some way was great,' Mr Gullino said. 'Although Venetians appreciate history, they don't study it.'

Betting on significant yes votes, Mr Zaia and Mr Maroni plan to launch talks with Italy's premier on 23 areas that are now the responsibility of the state, including security, migration, education and environmental policies.

They also want a greater share of the tax revenues, citing Lombardy's net contributions to the central government of 54billion euro (£48billion), and Veneto's of 15.5billion euro (£13.9billion).

Observers say they are unlikely to be taken seriously unless they get a huge majority of votes, something like 60% or 70%, on a strong turnout.

Any sense that Rome is dismissing the autonomy demands could play into the hands of the independence parties.

'Those who want separatism from the Italian state are in a minority,' said constitutional expert Luca Antonini of Padova University's law school.

'However, if the idea of autonomy is betrayed by the central government, it will feed the push for independence.'