Everseal brought proceedings against DMS on 27 November 2013 for alleged infringements of its patent for a mailer with self-adhesive closure (UK Patent No. 2,340,073), which was registered by Jonathan Horler in February 2000 but later assigned to Everseal.

The patent, the application for which was filed in July 1998, concerned a "new and useful business form or mailer...which uses, as the or each adhesive region, a non-tacky layer of a dry self-sealing contact adhesive which self-seals irreversibly...under finger pressure".

Other types of adhesive used at the time were either tacky in nature and incorporated a strip of material covering the adhesive layer ('peel-and-stick' mailers), required water-activation ('lick-and-stick' mailers), or used a contact adhesive that required a high-pressure sealing machine or a high-temperature sealer to seal the mail in its closed form.

Everseal had previously won a legal action brought against it by Mastermailer in December 2011, in which Mastermailer sought a declaration that a mailer supplied to it by DMS did not infringe Everseal's patent, and a subsequent claim for revocation of the same patent.

In its legal action against DMS, Everseal alleged infringement of its patent by three DMS products including the mailer from the Mastermail case (supplies of which had stopped in June 2013) and two additional mailer products manufactured and sold directly by DMS.

DMS successfully counterclaimed for revocation of the patent on the grounds of lack of novelty and lack of inventive step.

His Honour Judge Hacon ruled that the original mailer would have infringed part of the patent, were the patent valid.

However, the patent was ruled invalid on two grounds: for lack of novelty over the V-fold Readymade Mailer, which was manufactured by Moore Paragon, distributed in the UK by Laser Business Forms and sold in the UK by Viking Direct for a three-month period in 1995; and for lack of inventive step over two US patents (Fatlin and Johnsen).

Neither of DMS's additional mailers (developed following the Mastermailer judgement) were judged to have infringed the patent, were it to be valid.

Ray George, managing director of DMS, said: "We were accused of infringing [Everseal's] hand seal patent and it was ruled by the Judge that our Masterseal and Easiseal forms did not infringe the Everseal patent.

"We were also successful in our court action in proving that the Everseal patent was invalid. This means that we are now able to supply our hand seal forms to our customers without any further legal challenges from Everseal Stationery Products."

It is not known whether Everseal will appeal the ruling.