In the war against President Nicolas Sarkozy’s landmark pension reforms, Paul is an irregular soldier.

He is one of thousands of demonstrators and union hardliners who this week launched impromptu blockades of fuel depots, airport terminals, motorways and railway lines designed to cause maximum disruption to the French economy.

Standing on a grass verge with a few dozen comrades, Paul, who declined to give his full name, keeps a wary eye on the police checkpoint down the road. He spent the night blocking access to a fuel depot on the banks of the river Seine, in Rouen, north-west of Paris, before the gendarmes moved in to break up the picket. A convoy of re-provisioned petrol tankers rumbles past with much needed fuel for France’s service stations, a fifth of which had run dry on Friday.

But Paul is happy.

“There is a real excitement in this. It is almost joyful,” he says, quoting Spinoza’s dictum about joy as the source of power. For this is France and Paul is a philosophy teacher. “The pensions protest has managed to capture the scorn for Sarkozy,” Paul says. “I’m not here because of pensions. It doesn’t matter to me. I am here to make Sarko pay and to allow something to happen.”

That unpredictable “something” – the risk of rising social tensions even unrest – is what worries the French government.

It is also what partly explains why France is such a difficult country to reform. Much of the French media drew a contrast this week between the whimpers of protest in Britain against swingeing cuts and the howls of French indignation at a planned increase in the retirement age from 60 to 62.

Mr Sarkozy is determined not to retreat on the pensions overhaul, which has become a litmus test of his authority. Faced with the risk of contagion, the president is anxious to push through the reform as quickly as possible. On Friday, the Senate voted on the reform bill after the government used its powers to curtail debate.

A final vote by both houses of parliament is expected next week.

The government has warned about the economic damage from a protracted strike.

Construction companies, Air France, rail operator SNCF and road haulage groups have begun to count the cost of the strikes and fuel protests.

But the overall effect on economic growth is likely to be marginal, according to Eric Heyer, economist at Sciences Po university, who said austerity plans and the strength of the euro were a far bigger concern.

Despite this, unions are planning another day of strikes and mass demonstrations – the regular army in the pensions war – on Thursday.

The guerrilla-style tactics are also set to continue. With its oil refinery and fuel terminal, the industrial outskirts of Rouen have become an important battleground.

With the police manning the depot entrance, Paul and his comrades plan to block nearby roundabouts and roads instead.

“It is lamentable,” said Bruno, a tanker driver from Caen, as he waited at the recently re-opened Rubis fuel terminal. “Paralysing the economy like this is indefensible. Think of all of those small businesses on the brink.”

But most other drivers backed the protesters.

“They should be blockading many more places,” said François Bosquain. “I am not prepared to work longer. It is the thin end of the wedge. They want to dismantle our social rights and they don’t want to make the rich pay.”

Even those backing pension reform were just as likely to blame Mr Sarkozy for not negotiating a truce.

“I think we have a government that is too inflexible and too proud,” said a lorry driver waiting patiently in line at a truck stop to refuel. “It is necessary, but too brutal and too sudden.”

Despite the disruption, public sympathy for the protests movement remains strong. According to a BVA opinion poll published on Friday, 69 per cent of those asked approved of the strikes.

Public support has emboldened the strikers. “There is no particular sense of demobilisation,” said Stéphane, a technician at the Petroplus refinery, one of 12 refineries that are in the process of ceasing production.

“There are daily votes and each time there is a crushing majority to continue the strike.”