Watching the speed of Honda's progress with their engine and their performance in Canada made Red Bull's decision to switch "pretty clear cut", according to team boss Christian Horner.

An announcement was expected sometime before the end of this month with many expecting it would come at the company's home race in Austria next weekend, however, on Tuesday the news came that the Milton Keynes-based outfit will join junior team Toro Rosso as customers of the Japanese manufacturer.

Though potentially irking their long-time partner Renault, coming just days before their first home race in France in 10 years, Horner believes there was no reason to wait in announcing the switch once the deal was done.

"We decided that based on the information we had from Montreal – our decision, driven by engineering, was pretty clear cut in the end," said the Briton.

"We've been in a privileged position to have a front row seat to monitor the progress of how Honda have been getting on in our sister team at Toro Rosso versus our own power supply.

"It's been great to see that progress. We've come to the conclusion that Honda are making good strides, good progress on both performance and reliability, and therefore we've made the difficult decision to change power units after 12 seasons to something new for 2019 onwards.

"Renault were also very interested to have a decision as soon as possible to get their own plans in place, the timing was right to make that commitment, make that decision, and hence the announcement today."

With the experience of McLaren's difficult three-year project with Honda still fresh in all minds, some are wondering if this could spell doom for Red Bull and their hopes of fighting for the championship.

"We've been trying to do that over the last couple of years, and of course the power unit is a vital element within an F1 car," the team boss stated.

"We're confident that Honda have the right infrastructure, the right resources, the right technical capacity and determination to help us in our quest to reduce the gap to the teams ahead of us, Ferrari and Mercedes."

Masashi Yamamoto, Honda's motorsport chief, is also confident Red Bull can depend on him and his team to allow them to remain competitive at the front.

As a starting point, we do not want to see Red Bull Racing’s performance drop below its current level, but our target is to go further and do better than they are doing at the moment," he said.

“[Red Bull] has won several championships and this year too it has already won some races. In addition, it is also obvious that they have a very good chassis.

"This means we’ll have better chances of winning races. This gives further motivation to all the members of Honda, but at the same time, it is a huge pressure and responsibility for us.

"It is Honda’s nature to always aspire to a very high target, and I think that’s what makes Honda, Honda."