Boris Johnson was under mounting pressure on Saturday to overhaul holiday quarantine rules and compensate those caught out while abroad, amid growing concerns over rising cases of Covid-19 in France.

A cross-party group of senior MPs, scientists and trade unions said that holidaymakers already staying in a country that has been added to the quarantine list should be given statutory sick pay during their two-week isolation, in an effort to improve compliance and help those unable to work.

The calls come days after travellers arriving from Belgium, Andorra and the Bahamas were told they would have to quarantine for 14 days following an increase in Covid-19 cases. Spain and Luxembourg had already been removed from the travel corridor list.

Concerns now centre on France, where there were 2,288 reported cases on Friday, a steep rise from Thursday’s 1,604, following a 33% week-on-week increase between 27 July and 2 August. It has triggered fears that France could be added to the quarantine list. Hundreds of thousands of holidaying Brits could be affected were that to happen. Norway has announced it is reimposing quarantine restrictions on the country.

Senior MPs are now calling for those already abroad when told to quarantine to be compensated for the two weeks they spend isolated upon their return. David Davis, the former Tory cabinet minister, said: “If the government changes the rules while you’re away, and it costs you two weeks’ work, then it’s the government’s responsibility. Truth be told, if they don’t do it voluntarily, a smart trade union will take them to court anyway.”

Nick Thomas-Symonds, the shadow home secretary, said: “Following the mass confusion around the decision on Spain, there should now be plans in place to support people coming home where there is no guarantee their employers will allow them 14 days of work flexibility.”

The acting leader of the Liberal Democrats, Ed Davey, said: “If the government wants people to quarantine, then they must make sure people have the financial means to do so.

“Rishi Sunak should not be leaving people in a position where they’re choosing between quarantining or putting food on the table. The chancellor must step in and grant sick pay for all those returning from a country where the rule has changed while they were there.”

Frances O’Grady, the TUC general secretary, said: “No one should suffer financially for following official advice to quarantine. It’s not holidaymakers’ fault if guidance changes. Wherever possible, employers should do the right thing and pay quarantined workers their full pay, but we also need the government to step up.”

Just 10 enforcement orders have been issued to people who have broken quarantine rules after arriving in the UK, provoking concerns that the current system is not being properly enforced.

Scientists stressed the dangers of not helping people. “If people are caught by the government changing its quarantine regulations, and ordered to self-isolate, many may be tempted to keep silent about that and quietly go to work without admitting they should be self-isolating – just to make ends meet,” said Paul Hunter, professor in medicine at East Anglia University.

“I think that if you are actually forcing people to stay off work for two weeks, then they should at least get sick pay.”

Stephen Griffin, associate professor at Leeds University’s school of medicine, said: “They want people to travel and support the air and travel industry, but they are not prepared to help those individuals if they get caught when quarantine is suddenly imposed by ministers. That is simply unfair.”

Quarantine will only work if it is adhered to, added Andrew Freedman, of Cardiff University School of Medicine. “This depends on effective enforcement which does not appear to be the case at present, as well as cooperation from those required to quarantine,” Freedman said.

There is already mounting anger on the Conservative benches over the blanket quarantine policy, with MPs asking for testing to be used at airports or quarantine measures only applied to more specific areas. Davis said: “Other countries have been using tests for a while. There are some fast systems being used. There may be some dispute about how accurate they are, but it is a lot better than ruining people’s jobs and lives.”

Graham Brady, chairman of the 1922 Committee of backbench Tory MPs, and former party leader Iain Duncan Smith last week called for a proper testing regime for air travellers to be implemented as quickly as possible.

Marseille announced on Friday that mask-wearing would be compulsory in the old port quarter between 10am and 4am, following the imposition of similar measures in parts of Nice and St Tropez earlier this week.

The British government has said it “will not hesitate” in adding other countries to the restricted list if necessary. Downing St sources said on Saturday that it was closely monitoring the situation in France. People who refuse to self-isolate for 14 days when required after visiting certain countries can be fined up to £1,000 in England, Wales and Northern Ireland. Those returning to Scotland can be fined £480, with fines of up to £5,000 for persistent offenders.

A spokesman for the Treasury said: “We’re dealing with a global pandemic and that does mean that there is a risk that travel can be disrupted. We keep quarantine rules under constant review. Anyone planning to travel should consider these risks. We urge employers to show flexibility where possible to employees who will have to self-isolate due to quarantine rules.”