THANK goodness for nail polish, I say. Not this spring’s must-have fashion predilection, to be clear, but the primary means to distinguish Laviai and Lina Nielsen as we chat on the ninth floor of one of Belgrade’s few non-concrete bunkeresque hotels.

The identical twins from east London will both make their senior debut for Great Britain and Northern Ireland today at the European Indoor Championships in the 400m and it seems entirely fitting that they will embrace the occasion together rather than apart.

Rewind nine years to Mayville Primary School and not a metre separated their initial excursion into the sporting sphere. “We had a track in our playground,” Laviai recounts. “And the first lunchtime it opened, we stepped on the track together.”

One was better. Then the other. A continual trade, borne out of natural athleticism. “Our teachers didn’t let us do more than one event on sports day,” Lina reveals. “We went to a girl’s school so it was kind of strange we were sporty. We were outsiders in that sense so it was nice we had each other.”

There was ready stimulus on their doorstep, however, as their home is about a five-minute drive from the Olympic Stadium in Stratford. As London 2012 approached, their applications to volunteer were eagerly submitted. They have come a long way since.

“I kit carried for Jessica Ennis-Hill in the 200m of the heptathlon,” Laviai recalls. “That changed our outlook on sport because the support that the British crowd gave to Jess was just incredible. We never took sport seriously, but once we saw that, that was the game-changer.

“That winter was when we started training. It was something that just clicked in our heads.”

Room-mates here in Belgrade, their training is still undertaken in tandem even if their academic interests have diverged since the pair achieved identical A-Level results, with Lina studying for a degree in chemistry and her sibling in geography. Otherwise, they are the proverbial peas in a pod, trading in-jokes in private code, completing each other’s sentences and profiting from a closeness deeply invested in mutual support.

Never once, Lina says, has one sulked or stropped at a loss in their head-to-head series. “I don’t feel like we compete against each other. It’s strange because when we go into the arena, it doesn’t feel like she’s my twin sister. You forget about it and focus on everyone in the race. When you’re competing against some big names – like against Zuzana Hejnova in Birmingham – it’s just the person in lane six.”

Laviai, the reigning European junior 400m champion, has the clearest hopes of an individual medal this weekend in an event where the top three in the rankings are all on sabbatical from the 400m hurdles. Eilidh Doyle is amongst them but will soon be challenged by Lina who will cross over with intent this summer in a quest to become the Scot’s successor-in-waiting.

“She took a lot of convincing,” Laviai confirms. “My coach and I were like, ‘Come on you need to do it’. We’ve got different strengths, I can move my legs a lot quicker but Lina has got bags of endurance, which is what you need in hurdles.”

Doyle views the extra competition as healthy. “It’s great that she’s doing it,” the Olympic medallist acknowledges.

All three will link up come Sunday night when the British squad chase yet another 4x400m relay gold at these championships. “We always joke that the Nielsen family make up half the relay team,” Laviai says. Identically driven, that would seem a gag that’s destined to run and run.

Meanwhile Guy Learmonth wants to secure a medal in the 800m this weekend to prove his gamble to swap the lavish facilities of Loughborough for a rough and ready set-up around Berwick is destined to pay out. The 24-year-old has substituted UK Athletics base for running up hills and along the banks of the Tweed and with his career resuscitated, he hopes to produce in the Serb capital.

“It’s just to prove to myself that I can do it, to deliver a big performance,” he said. “It’s the next step up I need for my career and also to prove to myself, and other people, that the move home was right, that you can swim against the tide and do things your own way.”

Meanwhile UK Athletics have confirmed they will not cut ties with controversial coach Alberto Salazar, despite fresh allegations linking the American – and Mo Farah – to the misuse of prescription drugs, until an investigation by US anti-doping authorities is complete.

“Their statement was, that until an anti-doping process has been completed and the findings have been confirmed then we shouldn't make those assumptions,” UKA performance director Neil Black said. “And I think that is perfectly reasonable stance.”