Image copyright Reuters

From the moment Donald Trump's election victory was confirmed on 9 November, all sorts of businesses have had to keep alert to the fallout of a result they didn't expect.

And it seems there's been a surprising impact on the toughest business of them all - love.

Use of online dating site eHarmony spiked by 35% in the US in the days that followed the Republican's victory.

Businesses don't like uncertainty, goes the mantra. Well, nor, it seems, do those looking for love.

Grant Langston, chief executive of eHarmony, told BBC Radio 5 live's Wake Up To Money that the increase in activity on his site was reminiscent of those seen after the 9/11 attacks.

"You see a spike in usage after Donald Trump and people's desires to be in a relationship, so if they're in a bad relationship they don't want to leave, and if they're not in one, they want to get into one.

"November is usually a pretty low season, and we saw a tremendous spike in usage after the November 8 election. When 9/11 happened we saw a similar change in people. When times get unpredictable, they just want to be with someone."

Tinder effect

It's not only a changing political climate that is keeping eHarmony and its customers on their toes. Since the company was founded 17 years ago in California, the dating site now has many more competitors, with one in particular changing the landscape.

"Tinder has made 20-somethings want to participate in online dating. Prior to that, it wasn't something that interested people in their 20s, they thought online dating was sad," says Mr Langston.

Image copyright EHarmony/Twitter Image caption eHarmony has had to move with the times, for instance by updating its communication process

But he also sees Tinder's emergence as an opportunity for his business, which asks people to fill in long questionnaires in the hope of finding a long-term match. "People in that age group come into the market, then we catch people who aren't satisfied with the Tinder experience or are more interested in a more meaningful relationship."

Although he hasn't followed the "swipe left" style of Tinder, eHarmony has had to adapt as a result.

"The mechanism of delivering that service has got to change, and we've changed it a lot. The communication process, where you swap messages, was quite antiquated, and we've made it much more like text, immediate and very easy."

While Donald Trump may have got those looking for love logging in, has that other first-date conversational taboo - Brexit - had much of an impact on eHarmony and its choice of European headquarters?

"For now we're ok with [our London office]," Mr Lagston says, though he adds, "there is always a chance we could move it to Frankfurt or some such place."