Mercedes finally look like they're back in business after Sunday's Spanish Grand Prix secured them back-to-back victories.

Ferrari and Sebastian Vettel had taken the opening two races, with Red Bull's Daniel Ricciardo coming from behind to win in China, but Lewis Hamilton has finally managed to pull away at the top of the standings.

Valtteri Bottas picked up 2nd place in Spain as Mercedes dominated - although it didn't come about smoothly.

Pirelli changed the tyres ahead of the race to be much thinner, sparking accusations that this was done at the request of Mercedes to give them an advantage.

Team boss Toto Wolff has already denied them once but victory has only strengthened their rivals' claims.

Red Bull, in particular, have taken issue with the change with advisor Helmut Marko speaking out.

The Austrian firmly believes there's a very good reason why Mercedes could request such an advantage from Pirelli - and it's not fair on other teams.

"When you're a team and a manufacturer at the same time, you can do that," said Marko.

"We [Red Bull] produce energy drinks - of course we cannot influence as much compared to a maker of passenger cars."

But Wolff has been quick to respond to the accusations, dismissing the idea that there was any collusion.

"It's not the first time the doctor [Marko] sees ghosts," he said.

"There were problems with blistering on the tyres in the winter tests, even at Red Bull. The rears looked like a volcanic landscape. So Pirelli improved them. It's bad for business if tyres explode."

As for Red Bull's complaining, Wolff also had some very strong words for their targeting of his team.

"I think it looks weak if you have a bad weekend and complain," said Wolff. "First and foremost, we look at ourselves for our problems."

Wolff certainly has a point, too, as both Ferrari and Red Bull suffered problems that prevented them from putting up a proper challenge.

Daniel Ricciardo found himself well off the pace after a spin on turn 10 that wasn't caught on camera and wasn't able to recover for an assault on the podium.

Sebastian Vettel, on the other hand, controversially pitted twice when everyone else settled for one, costing him precious time.