Kevin Harvick has revealed that NASCAR President Mike Helton has personally told him not to get into any more on-track altercations with Kyle Busch, following a stormy recent few months between the two drivers and between Busch and Harvick's Cup team owner Richard Childress.

"I was told a few weeks ago that if we touched the #18 car, we'd be parked," confirmed Harvick bluntly, after letting slip over the team radio during Saturday's New England 200 Nationwide Series race that he was having to be extra careful when the two of them ended up running together at the front.

"I've just got to be really careful. I would have liked to have gotten the track position and slid up and do what I needed to do," he said. "But I've just got to be really careful. That's the way NASCAR put it to me.

"It would have been a lot easier to win if you didn't have handcuffs put on you, but that's the way NASCAR said we had to do it," he finished.

NASCAR would not comment on whether or not Harvick had been warned off, saying that any conversation between Harvick and Helton was a private one, but NASCAR Vice President of Competition Robin Pemberton said that "It's our deal to keep law and order on the race track," while adding that he wasn't personally at any such meeting between Harvick and Helton.

But Kyle Busch confirmed that he had certainly not received any such warning. "If he got a warning, I'm sorry he got a warning. I did not get a warning. So I do not know that I took advantage of him in any way."

"I raced hard, I raced clean and I ended up where I am," he said in Victory Lane after taking his 100th national-level NASCAR race win. "I had a great race with Harvick - no problem ... I think that's the way you should race. I raced him just as clean as he raced me, which is great."

Both drivers had been put under probation for a month after a controversial confrontation between the two drivers on-track and in the pit lane area at Darlington mid-May. Four weeks later, team owner Richard Childress stormed into Busch's garage at Kansas and proceeded to punch the 26-year-old owner-driver after a minor bumping incident during the evening's Camping World Truck Series, for which Childress was fined $150,000 and put under probation but Busch was exonerated of any blame that might have affected his own prior probation.

The following weekend at Pocono, Harvick had seemed to go out of his way to try and antagonise Busch on track at every opportunity early in the race, but Busch stubbornly refused to rise to the bait on that occasion.

"He knows he has one coming," Harvick told afterwards on that occasion. "I just wanted him to think about it."

It seems to have been this provocation that earned Harvick the private warning from Helton the following week at Michigan, as NASCAR sought to balance the public policy of "Boys, have it it!" with the legitimate safety concerns for all those involved if two drivers are deliberately trying to wreck each other at speeds approaching 200mph.

However the idea that NASCAR are handing out warnings and instructions to drivers in secret will not be popular with fans who want to see more transparency in the series. It emerged recently that Denny Hamlin had been secretly fined $50,000 for criticising NASCAR on Twitter, while Ryan Newman revealed that he had also been secretly fined in April 2010 for critical comments he made about the style of racing at Talladega.

There have also been strong rumours in the NASCAR paddock that Newman was secretly fined a further $50,000 after allegedly throwing a punch at Juan Montoya during a meeting in the NASCAR hauler intended to patch over an on-track incident the previous week at Richmond. The reports say that NASCAR imposed the secret fine in order to head off threats of Montoya mounting an embarrassing public lawsuit against Newman.

Although quoted Montoya at the time as saying "Newman hits like a girl", both drivers declined to either confirm or deny the rumours of either the original altercation or any subsequent fine: "I don't know, ask him," said Montoya. "I could tell you either way, couldn't I? I could make something up. Let's leave it at that."

"That's just speculation," Newman had said in turn. "It was a private meeting. That's why we had it at the hauler. With conflict there are varying opinions, that's what causes the conflict. I'm past it."

NASCAR insisted that whatever happened between drivers and NASCAR in private in the NASCAR hauler was to remain private: "Anything relevant to discussions that NASCAR has with competitors in the hauler will continue to stay between NASCAR and the competitors, and NASCAR will always work to protect that bridge of confidence," NASCAR spokesman Kerry Tharp had insisted.

NASCAR are taking a similar line over the latest revelations from Harvick and insisting that it's a private matter on which they will not comment, and NASCAR Vice President of Competition Robin Pemberton pointed out that drivers and team members were often talked to by officials and advised what could happen if their actions continue.

"You might talk to a driver, crew chief or crew member from time to time to say, 'Hey, look, just remind yourself what you're here for and what you're doing,'" said Pemberton. "That's not anything different than what goes on with anybody.

"In all honesty, I wasn't at one of those parties, so I wouldn't comment [on specifics in this case]," Pemberton said. "[But] when it bleeds over into the sport and could potentially take innocent competitors out of races and their opportunity to compete, at the end of the day we rule inside the race track and inside the walls and it's our job to try to protect those that may be affected by this and not their own doing.

"They're good competitors out there," he added. "They all know what they can and can't do."