England are wary of being dragged into an unwanted power struggle with Alastair Cook ahead of the summer Test series against Sri Lanka and Pakistan after he ignored new regulations by wearing an old-style helmet that fails to conform to new safety standards.

Nevertheless, Cook's insistence that he must be the ultimate judge of his own safety puts the ECB in a delicate position as it seeks to enforce the adoption of a modern helmet design across the whole of the first-class game.

All eyes will be on Essex's next Championship game against Sussex at Hove, beginning on Sunday and, as long as England's captain remains true to the old design, it is likely that the rebellion will be extended to more batsmen possessing similar misgivings.

Cook ignored the stipulation during Essex's opening Championship match against Gloucestershire at Chelmsford - preferring to stick an Essex badge over his old England helmet, which dates back to the 2013 design and does not comply with the latest British Safety Standard BS7928:13.

The new design of helmets have a narrower gap between the peak and grille and are not adjustable on each side so reducing the likelihood of a ball bursting through the opening.

ECB officials contacted Cook on Thursday to remind him of the new regulations after they were beset by enquiries from within the game about his decision.

Although Cook has yet to explain his reluctance to use the new helmet publically, he has made his reservations plain in private and has had meaningful conversations, among others, with the director of England cricket, Andrew Strauss. His county, Essex, are thought to be sympathetic towards his predicament even though they as well as Cook could be viewed as culpable in any ECB disciplinary hearing.

Only if Cook finds a new helmet that he is comfortable with will he feel able to make the change and he has already tried several manufacturers in a so-far unsuccessful attempt to find an approved helmet which he feels gives him an uninterrupted line of vision. Further trials were expected to follow in the nets at Hove on Sunday and, should he opt for a different manufacturer, an awkward meeting with his kit sponsor lies in wait. The choice extends to nearly 30 helmets from eight brands.

He received immediate support from his Essex and England team-mate Ravi Bopara, who was critical of the inflexibility of the new design.

Bopara told Sky Sports News: "I understand where Cookie's coming from. Because of the safety aspect, with everything that has happened… we are told we have to wear the helmets that meet the standard guidelines.

"But it is difficult for players to change helmets like that, because you [get] so used to wearing a certain helmet which you're comfortable with - and you have your visor as wide as you want it.

"But the problem with the new helmets is you can't move the visors - you've just got to look at the hole that's there. Sometimes, that bar that goes across can get in the way."

Cook, far from being blasé about his safety, has had discussions with England colleagues about the risk versus reward benefits of the new designs. Although no batsman can ever regard themselves as safe from injury, he has been one of the most decisive players of the short ball in world cricket. Anything that disturbed that split-second judgment - such as the suspicion that he was losing the ball in flight - would be bound to have a detrimental effect.

Cook therefore finds himself - however unintentionally - cast as a potential poster boy for personal liberty and, in the event that his search for a satisfactory helmet remains unrewarded and he feels obliged not to conform, the ECB will be left in the unfortunate position of either having to call him before a disciplinary committee, or respecting his wishes and seeing their new policy immediately undermined by England's Test captain.

Such concerns affect players of all standards and the fact that helmets are mass produced in a limited number of sizes while the human face comes in many different forms does seem to be an argument for a grille that can be adjusted to some extent even without taking personal preference into account.

An ECB spokesman told the Times on Friday: "These regulations were drawn up after extensive consultation with the Professional Cricketers' Association, and all the England players were given a further reminder of the importance of this issue earlier this week.''

The umpires at Chelmsford, Jeff Evans and Michael Gough, were aware that Cook was using what is now, to all intents and purposes, an illegal helmet, but despite reports to the contrary they are not empowered to enforce the new regulations by banishing him from the field.

They can only insist that a helmet of some type is always worn against all styles of bowling. If a player wears a non-compliant helmet, they can report the matter to the ECB or even refer the case to the Cricket Discipline Commission (CDC).

The ECB, recognising its responsibility to maximise player safety, imposed new helmet regulations last November after a number of disturbing, high-profile incidents, including a blow to the eye that ended Craig Kieswetter's career and a broken nose for the England fast bowler Stuart Broad in a Test against India.

But a mass expression of concern about the practicality of the new designs - not just by Cook but by others who may follow his lead - could force the ECB into allowing old helmets to be used until a further period of research and reflection is carried out. The fact it is Cook, of all people, who has been caught up in the changes makes punitive measures unlikely.

At least one county wicketkeeper is also reluctant to follow instructions to wear a helmet whenever standing up the stumps and has asked whether he can sign a disclaimer.

The ECB's published regulations on helmets read: "It shall be the joint responsibility of each relevant participating cricketer and the first-class county, team owner or club (as applicable) for which he/she plays to ensure that he/she wears compliant headgear at all times when undertaking any regulated activity in any match.

"Notwithstanding the umpire powers pursuant to Regulation 4, in the event that a relevant participating cricketer is alleged to be in breach of Regulation 3 or fails to act immediately on an umpire's instruction to wear a head protector or face mask (as applicable) pursuant to Regulation 4, the relevant participating cricketer and his/her first-class county, team or club (as applicable) may be referred to the CDC for disciplinary proceedings in accordance with the CDC regulations."