Following his exit from Manor's F1 operation at the end of 2015, Booth briefly returned to F1 with Toro Rosso two years ago to help work its drivers and team operations.

But with Manor having ramped up its efforts in sportscars after stepping up to the LMP1 category, Booth has decided to step back from F1.

Speaking exclusively to Motorsport.com, Booth said: "Let me put it this way: My involvement with Toro Rosso came to a natural end. Maybe I look too old for Formula 1 now. Is that enough?"

Booth denied suggestions that his exit had anything to do with Honda's arrival as a team partner and the fact it was throwing more resources at the project: "Let's explain it this way: At my age, you get tired of all these flights and hotels and so on.

"On the other hand I like to travel privately... I might even go back to Japan sometime."

He added: "From now on I will fully concentrate on our program in the LMP1 class. We have a lot planned, even though we won't have a chance against Toyota.

"We don't have a hundred million euros. And in the LMP1 it's the same as in Formula 1: you can buy performance."