While not all of Max Verstappen's - or Daniel Ricciardo's - DNFs this season have been engine related, a good few have, as have the various issues in practice sessions and qualifying and the resultant penalties.

With the French manufacturer insisting that there will be no further major upgrades this season, only small ones, Christian Horner has hit out at Renault claiming that it isn't delivering the performance or reliability that should be expected.

"Renault are quite aware that their reliability and product isn't where it should be," he told reporters in the wake of a race in which despite Verstappen's early exit, an audacious move by Daniel Ricciardo salvaged yet another podium for the Austrian team.

"It's their business to sort that out," he continued. "We're a paying customer and it's obviously below par the service we are seeing at this point in time because of the reliability issues, the failures.

"We pay a hell of a lot of money for the engine," he fumed. "They need to sort it out because it's hurting them as much as it is hurting ourselves. At this level, you can't afford the kind of failures that we're consistently seeing.

At a time the French manufacturer has admitted to having had talks with McLaren in terms of an engine supply, a move which would need the blessing of the FIA, Horner insisted: "Reliability across the three (current) teams is pretty dire... turbo failures with Kvyat, engine replacements that have had to happen with two cars as we come here.

"It's not great, it's far from great," he continued, "and it's not the level an engine supplier which wishes to be competitive in F1 should be at. They are working hard at it and hopefully putting in place process to avoid the kind of issues that we are seeing."

Horner's comments are the latest in a long line of attacks from Red Bull which has struggled with its Renault engines ever since the new formula was introduced in 2014.

Endless threats to withdraw from the sport, at one time forcing Bernie Ecclestone and the FIA to intervene and seek a new supplier - but to no avail - have met with little sympathy from fans or rivals, Mercedes and Ferrari both refusing to supply current spec units to a team they know has everything else in place to mount a serious challenge.

Check out our Sunday gallery from Spa, here.