Horner has taken aim at F1 title rival Mercedes’ superior straightline speed at recent events and questioned the legality of the W12, claiming its rear wing had “score marks” on it in Brazil. 

Red Bull has threatened to protest Mercedes if it continues to see further signs of what it believes to be a rear wing illegality across the final three races of the season. 

Horner revealed that the FIA has introduced more stringent load tests following qualifying in Qatar and noted that Mercedes’ straightline speed advantage had reduced around the Losail International Circuit. 

"I think the load test has done its job, because their straightline speed is under control," Horner told Sky. 

"So suddenly, we're line on line. We haven't seen that for about four or five races. 

“As I said before, this is all about not so much this circuit, but it's very much about Jeddah and Abu Dhabi where there's a massive premium on straight line speed.”

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Horner conceded that while Mercedes’ straightline speed was closer to that of Red Bull’s in qualifying, he felt Lewis Hamilton ultimately pulled off a brilliant lap to take pole position by nearly half a second. 

"I think their straightline speed has come down a bit," Horner said.

"I think that it looks very similar to our straight line speed now, which is good to see. I think Lewis made all his time in Turns 6 and 7. 

“Particularly on that last lap, he had an amazing sector through that sequence of the two slower corners. 

"So, from what we seen on the straight line speed, it looks normal. So, just a very strong lap by Lewis."