Despite Toro Rosso being renowned as a breeding ground for emerging talent, the team took a gamble in hiring two very young rookies in Verstappen and Sainz.

Signing Verstappen, in particular, was criticised given he was only 16 and in his first year of car racing at the time.

Key, however, believes the duo have proven everyone wrong.

Speaking to AUTOSPORT, Key said: “How can you lambast somebody for being too young?

“It’s ridiculous. It’s about driving at the end of the day.

“We had a bit of scepticism thrown on us, people saying, ‘How are you ever going to cope with two rookies?’

“But we said, ‘You know, we will be fine’, and they’ve been a very good story for the year.

“Their maturity and ability when it matters to get the performance out of the car – in a way a lot of rookies can’t always do – is really good.

“They also drive very differently. They do their own thing, which is good because they have each other to bounce off, they can see what the other guy is doing and try and respect that.

“The really positive thing for the whole team, and for them, is that they are pushing each other. They are both very closely matched.”

Key feels Verstappen has proven Toro Rosso was within its right to provide him with a 2015 race seat, and that he deserves to be in F1.

“Max is very aggressive, but in a good way rather than a crazy way,” added Key.

Sainz, Verstappen, Toro Rosso“He’s a very talented guy and has more than proven himself. He’s very brave and very quick.

“But sometimes he gets frustrated. You can see the emotion coming across.

“So there’s some maturity to come as he gains more experience and learns more about how the sport works, but he has the ability to do that, there’s no doubting that.”

By contrast, Key claims Sainz is a more composed figure who is able to keep his emotions in check.

“He has been very smooth, very disciplined,” said Key.

“You can see that when the pressure comes in, he keeps a cool head.

“One thing with Carlos that has struck me is how cool, calm and collected he is, and how analytical he is if something goes wrong.

“He’s very strong, very observant, and you get a lot of philosophical comments if something doesn’t work out. If he makes a mistake he will apologise for it.

“Overall he’s done really well and probably surprised a few people, and I’m glad he has because he absolutely deserves it.”