Tunisia was the birthplace of the Arab Spring in 2011 and the country where a democratic transition seemed most secure.

Yet over the past year we have seen the assassination of two secular opposition leaders, Chokri Belaid and Mohamed Brahmi, and growing opposition to the government elected in 2011. Why?

Abdelaziz Messaoudi of Tunisia's Ettajdid Movement - the successor to the old Tunisian Communist Party - says the government faces a real legitimacy crisis.

"The Constituent Assembly elected in October 2011 had one principal task - to draft a constitution by October 2012," he says.

"This it has not done. And no end date has been set.

"On the contrary the government now says that the Constituent Assembly provides a legal basis for government and general legislation."

The government - led by the Islamist Ennahda Movement - has demonstrated "total ineptitude both economically and politically."

Its actions seem more preoccupied with consolidating its own power than ushering in a new democratic era for Tunisia, Messaoudi argues, pointing out that almost all its nominees for local governorships are linked to the party somehow while civil servants, business leaders and security chiefs have been appointed on the same basis.

And it has failed to scrutinise the actions of more radical Islamist groups or make any attempt to prevent them from resorting to violence in the name of their sectarian creed.

"The Salafist movement which promotes jihad has been free to accumulate stockpiles of arms and run training camps for their use," he says. "It is this freedom that has enabled it to carry out political assassinations of both the democratic opposition and members of the army and police."

The opposition has repeatedly called on Ennahda to take action against the groups behind such terror tactics, but to no avail.

"Even after the assassination of Brahmi on July 25 attacks on soldiers in the jihadi-controlled Chaambi mountains have escalated. Leaders of civil society organisations continue to be threatened with assassination.

"The arrest of a number of leaders of Ansar Asharia ("defenders of sharia") has exposed its wider plans for the destruction of the Tunisian state and the creation of an Islamic emirate under sharia law. It has also demonstrated links between this organisation and al-Qaida."

Popular anger over this has led to massive rallies demanding the government's resignation.

It sounds similar to Egypt, where the Tamarod ("rebellion") movement led mass protests and gathered millions of signatures for the overthrow of Mohamed Morsi's Muslim Brotherhood-backed government.

But Messaoudi doesn't see the situations as analogous.

"The only similarities are that both countries are in a process of democratic transition and in both Islamist governments have presided over a catastrophic deterioration in the lives of ordinary people," he says.

"Economically there has been galloping inflation, a collapse in investment, rising unemployment and a sharp decline in purchasing power that has hit the middle strata as well as workers.

"Politically the Salafist groups seeking to impose their control over society through intimidation and force are on the rise.

"But in Tunisia the army has not played any visible political role. Unlike Egypt, there is no tradition of army involvement in political life, and democratic forces in Tunisia have called on the army not to intervene and to restrict itself to defence."

But it does seem that in both countries political Islam has been able to win power through elections. What's its social base?

"Political Islam has never been absent," Messaoudi explains. "In Tunisia, as in Egypt, the national liberation struggle was waged under the banner of nationalism and led by elites who championed the modernising ideals of the Western enlightenment. The traditionalist Islamist forces did not represent the determining force.

"In Tunisia there was a bloody struggle over the nature of the post-colonial state, with the modernising forces challenging traditional hierarchies, abolishing polygamy, recognising the right of women to choose husbands and to divorce and introducing universal education."

But political Islam was quick to reassert itself.

"The wave of reform associated with [first Tunisian president Habib] Bourguiba soon exhausted itself and the problems inherent in personal power became more apparent in the 1970s, as his regime sought to face down a student movement inspired by Marxist and progressive ideas.

"This anti-democratic tendency reached its peak under Zine el-Abidine Ben Ali, while the revival of Islamist forces benefited from the Iranian Islamic revolution and the mobilisations against Western interventions in Lebanon, Afghanistan and Iraq.

"The social base of political Islam has always been among the most traditionalist sectors of Tunisian society, those who feel threatened by capitalist globalisation. But fierce repression under previous regimes provided it with a hardened cadre force that earned popular respect through its apparent lack of corruption.

"At the same time the progressive democratic forces were divided among many parties, and in 2011 they were unable to take advantage of the collapse of Ben Ali's regime.

"Today the situation has changed. Current opinion polls indicate that Islamist forces would no longer be politically dominant."

But does that justify calls for the overthrow of an elected government?

"Any government has to be judged by its handling of the economy and its commitment to confront the massive political and developmental problems facing the Tunisian people.

"The government failed to produce a constitution and has presided over a coercive erosion of civil rights. Economically, every signal is set at red - all development is at a standstill.

"That's why we have seen hundreds of thousands demonstrating in the street on August 6, 13 and 24, and even greater numbers on September 7."

At the heart of these mass protests is a new movement, the Popular Front.

"This is an alliance of radical parties representing a spectrum of ideological positions," Messaoudi says.

"They range from the Workers Party - previously the Maoist-aligned Communist Workers Party - a number of small Trotskyist groups and progressive nationalist parties such as Brahmi's Popular Current and the Ba'ath Party.

"The Front has not yet published its programme, but its leaders have called for the nationalisation of a number of enterprises, the redistribution of land to agricultural workers and striking down the international debt accumulated by the previous regime."

But the Islamist forces are still strong. Among them are there any who could be brought on board to co-operate with secular forces in the national interest, or more specifically in the interests of the great majority of Tunisians, the working people?

"Unfortunately not many.

"Political Islam is divided into two trends. There is the Wahhabi trend, very influential in Saudi Arabia and some of the Gulf states.

"Then there's the Muslim Brotherhood which emerged in Egypt in the 1920s and which is also funded by a range of Arab and Muslim countries.

"Both are fundamentally conservative and dream of returning to the social 'norms' of the seventh century.

"Those who support an open, tolerant Islam are less numerous, lack the same level of organisation and - above all - do not enjoy the enormous financial subsidies from the Gulf states that sustain the two reactionary trends."

It seems that in Tunisia, further confrontation between the Islamists and the left is not going to go away.