Sporting a new upgrade to the car, reigning double world champion Sebastian Vettel was streets ahead of his rivals in qualifying at the European Grand Prix in Valencia 12 days ago.
In the race Vettel was then around a second per lap quicker than any other car on track, opening a 20-second cushion by the time the safety car was introduced on lap 28.
An alternator issue then robbed Vettel of victory, but team-mate Mark Webber at least salvaged something for the team by finishing fourth after starting 19th.
The likes of McLaren duo Lewis Hamilton and Jenson Button, along with Mercedes' team principal Ross Brawn, have expressed concerns as to Red Bull's latest turn of speed.
Events at Silverstone over the weekend will determine whether Red Bull have indeed stolen a march on their rivals, or whether what transpired in Valencia was unique to that circuit.
"Certainly in Valencia both drivers were pretty happy with the way the car performed," said Horner.
"If we can be competitive this weekend we will take more comfort from that looking ahead to the different types of circuits coming up over the rest of the year.
"But it's so hard to predict this year. At the start McLaren were quick in Melbourne and Malaysia.
"The one thing we can see this year is that it's hugely difficult to make predictions.
"To predict Fernando (Alonso) winning in Valencia, after Saturday evening (when he had qualified 11th), was almost unimaginable.
"But he drove a great race, things went his way, and he became the first double victor this year.
"It is so unpredictable, and it will continue to vary from track to track."
McLaren sporting director Sam Michael, however, cannot see any reason why Red Bull would continue at Silverstone to have the significant edge they did in Valencia.
Michael said: "To find a second per lap through changing some fairly secondary parts on the top surface on the floor, which is where we know they have changed, would be pretty impressive.
"When we arrive in Silverstone we will find out if that is the case, but I will be pretty surprised if they maintain a second-a -lap gap on the rest of the field."
Michael is expecting Silverstone to be more suited to McLaren, as was the case in Barcelona where Lewis Hamilton grabbed pole, only to be sent to the back of the grid for a fuel irregularity.
Michael added: "If we look back to Barcelona, we were almost six tenths (of a second) in front of them on the grid before we took the penalty.
"So looking at the type of track Silverstone is, we're hoping for a repeat of that."