Today’s deadline for companies to register .eu internet addresses has sparked an "international mass panic", domain registries have claimed, amid fears that British companies have set themselves at a disadvantage by failing to apply for the new virtual assets.

The .eu suffix, designed to rival America's ".com" addresses, was opened to the public this morning following a four-month period where large brands were given the chance to secure their trademarks online.

Users today reported that the main registration site, run by the European Union, was operating very slowly, suggesting that it was experiencing heavy use.

A number of companies have already lost their claims to their preferred pieces of cyberspace, underscoring the fierce competition for key online assets, which have been allocated so far on a first come, first served basis.

Land Rover was beaten to discovery.eu by the American-based Discovery Channel. Both companies got their applications in within four minutes of registration opening.

Ralph Lauren and Nestle both lost out on the polo.eu domain name to Volkswagen.

"The alarm bells should be ringing for any company which has yet to secure its trademarks in .eu," Jonathan Robinson, the chief operating officer of NetNames, a registration service that manages the domain name portfolios for over 30 per cent of the FTSE 100, said.

"As of today there’s no protection for companies’ trademarks and it is open season on the .eu domain name for competitors, domain name speculators and cybersquatters."

Cybersquatters acquire domain names linked to high-profile brands with the intention of later selling them to the brands’ owners at a profit. The four-month closed period was designed to limit opportunities for such speculation.

It is feared that British companies, which are lagging their continental rivals in the race for .eu addresses have now opened themselves up to exploitation.

German businesses account for the largest portion of applications – 28.6 per cent – while British businesses, with just 9 per cent of applications, trail both Dutch and French companies.

"The demand for .eu has been very strong but being first is the key and major brands such as Land Rover have already missed out," Mr Robinson said.

"It’s worrying that British businesses are so far behind their European rivals in protecting their brands online and over the coming months there are sure to be a number of high-profile, costly disputes which could so easily have been avoided."

European businesses have filed 330,000 applications applying for 235,000 different domain names. The remaining 95,000 are potential domain name disputes where two or more parties have claimed they have a prior right or trademark to use that domain.

Steve Witt, managing director of UKDomains, the domain registry service, said: "It has been crazy. The phones have not stopped ringing and our website is receiving a tremendous amount of visitors as people submitting their claims for their own .eu address."

Mr Witt said it was important for trademark owners to have submitted their applications as a .eu address would "protect their corporate identity, enable customers to remember their web address more easily, ensure search engines find the company more easily and give a company a strong European presence in the market place."

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