Patent – Infringement of patent. The claimant alleged that the defendant (BT) infringed two of its patents (495 and 790) concerning the methods for controlling the way in which an asymmetric digital subscriber line (ADSL) operated. The alleged infringement related to the system used by BT to monitor and control its ADSL network. The Patents Court held that, applying settled law to the facts, that 790 was valid and was infringed by BT's system and that 495 was valid and was not infringed by BT's systems. The Court of Appeal, Civil Division, dismissed BT's appeal in respect of 790 where there had been no error by the judge in his construction of the patent or finding of infringement. The claimant's appeal in respect of 495 was allowed as the claim which had resulted in a finding of non-infringement had been invalid, and the remaining claims had been both valid and infringed.