Red Bull Formula 1 team principal Christian Horner was left frustrated by the “shades of grey” nature of track limits rules during the season-opening Bahrain Grand Prix.

Reigning world champion Lewis Hamilton held off a late charge from Red Bull’s Max Verstappen to claim victory after a thrilling conclusion to the race that saw the two drivers separated by just 0.745s at the flag.

Verstappen had managed to find a way past Hamilton with four laps remaining as he swept by with an illegal overtake at Turn 4, before the Dutchman let Hamilton back through after Red Bull was ordered to hand the lead back by race control.

While Horner ultimately accepted the decision was technically the correct one, he was annoyed by its ambiguous nature. Track limits at Turn 4 had been heavily policed throughout practice and qualifying but was not initially monitored during the race.

However, Hamilton was warned at mid-distance by his Mercedes team that he was coming under threat of potentially receiving a penalty if he continued to run wide through Turn 4, leaving the reigning world champion confused.

“It was frustrating, we could see as soon as Mercedes started to push they just used that part of the track,” Horner said.

“We questioned with race control ‘if that’s the case, can we do it?’ Because when you’re in a nip and tuck battle, there’s a two-tenth advantage using that part of the circuit. So they did it lap after lap.

“The race director then asked them to respect the limits otherwise they’d get a black and white flag. Obviously Max ran wide on the pass there. It had been made clear before the race that if someone got an advantage by going out there, they’d have to give it back.

"He did that immediately and the team instructed him to do it following race control instructing us. With these track limit things, they’re always going to be contentious but we do need to just have a consistent situation.

“You can’t say it’s ok to use it in the race, but you can’t overtake out there. It should be black or white, it shouldn’t be shades of grey.”

But Horner defended Verstappen’s decision to let Hamilton re-pass him on the run to Turn 11, saying his driver made the right choice.

“We had an instruction from the race director to give the place back immediately - Max was very sporting and did that,” Horner explained.

"It was frustrating and Lewis had just enough to retain his position to the end of the race. There’s no guarantee that we could have got the five seconds if that had been the penalty. So he did the right thing.”

Asked if he felt Red Bull ultimately lost the race on strategy, Horner replied: “No, definitely not. Mercedes had very strong pace at the beginning of the race. We couldn’t create a gap to cover them and their degradation looked impressive.

“So Max could never get more than two seconds clear of Lewis, they pitted early for the undercut, we conceded track position. And going into the race we very fixed our strategy on a two-stop.

“So they obviously went early again on their last stop. We stayed out 10 laps longer. We had a better tyre for the final stint but unfortunately Lewis had just enough to be able to hold on.

“It’s tough to lose a race like that but we have to take a lot of positives out of the weekend.”