High up in the 19th-century edifice that forms the front of the Gare du Nord in Paris, Eurostar has found a new, grand perch.

The cross-Channel train service has a startling upgrade in store for its business travellers, the latest gambit to bolster a company that is right in the frontline of Brexit. Last week it unveiled a lounge designed to feel more like an elegant Parisian flat, all high ceilings and marble fireplaces, sofas and wide tables. A kitchen stocked with a buffet curated by the Anglo-French chef Raymond Blanc is also promised later this year.

Beyond lies a cocktail room, whose centrepiece is a sunken circular bar. It will serve an Angélique, which, Blanc advises, is the only drink that actually wards off a crise de foie and aids digestion. And of course there are plenty of places to work, if you get that far.

Investment at Eurostar is pressing ahead, even if the rail operator could be forgiven for feeling uneasy about running trains on the one fixed link between Britain and Europe.

The referendum came in an already difficult year for Eurostar, with bookings dropping away after terrorist attacks in Paris and Brussels. Strikes in the summer and the axing of 80 jobs followed: the company said that June’s vote had created uncertainty, and its ticket sales dipped again. What chance, then, with actual Brexit?

Eurostar’s chief executive, Nicolas Petrovic, is smoothly upbeat: “I’m an optimist.” €1bn has been spent over the past three years, mostly on a fleet of new trains, more than half of which are now in service. “Brexit or no Brexit, the traffic is only going to grow,” he says. “The economies of London, Paris and Brussels are more integrated than they have ever been.”

However, Petrovic has said in the past that he sees no upside to Brexit. Eurostar, 55% owned by the French national rail operator SNCF, says it benefited greatly from the EU establishing common standards for aspects of its business, from train operation to employment. Possible headaches lie ahead in recruiting and retaining its diverse, international staff.

Analysts are uncertain about the effects of Brexit. Gerald Khoo, of stockbroker Liberum Capital, says there could be upsides and downsides: “Fewer MEPs and civil servants going to Brussels – but if UK companies really do pivot towards Paris, that could also be a boost.”

Nicolas Petrovic with one of Eurostar’s new trains. Photograph: Martin Godwin/The Observer

A weak pound cuts both ways for a cross-border business, but Eurostar’s leisure travellers are still mostly Brits, who will need to shell out more.

Indeed, concerns exist in the minds of travellers. One Eurostar passenger, a UK-based French designer called Hiba, travels regularly between London and Paris for work and to see family, but says she is thinking of moving back to France. “It’s been fine, but now there are these silly questions, I’m wondering if it’s all going to be complicated.”

Etienne Koehler, a frequent traveller who works for Banque de France, has already relocated back to Paris after 10 years in London. “Better get ahead of the mood, I thought – there is already less opportunity in the UK.” He thinks “without doubt” there will be fewer travellers between the cities in future, although he’s enamoured of the new lounge. “Sometimes it’s nice to be chouchouté [pampered].”

Jonathan Warburton, a London-based banker for a French bank, who takes the Eurostar every other week, thinks Brexit won’t affect his travel unduly. “The bank might shift about 5% of its staff over, but London’s the hub, and where the talent is.”

News of a new Paris lounge is a bonus, he says: the old one has been “a bit of a bunfight – these strange swivel chairs facing each other”. Mainly though, Warburton values the train’s convenience. For all that its occasional disruptions make headlines, he says delays are far shorter and rarer than when he flies. He is not alone: the number of London to Paris flights is in decline, even at the financial district’s neighbouring airport, London City.

Petrovic, meanwhile, points to growing ties between France and Britain in the energy, tech and fashion sectors as reasons to be confident. Even Blanc, who admits to “a moment of deep pain” when he heard the Brexit vote, vows: “Regardless, we’ll carry on.”