Google filed a patent infringement lawsuit against BT Group companies in a court in the US stating it was defending itself against the British communications services company's own "meritless patent claims" and its arming of patent trolls.

The company is understood to have filed a complaint against BT in the UK as well.

The move by Google comes about a year after BT sued the internet company for alleged infringement of six of its patents in a court in Delaware.

In a complaint filed yesterday in US District Court for the Central District of California, Google has sought remedies from four BT Group companies for the alleged infringement of four of its patents, relating to quality of service technologies and internet telephony gateways.

Besides a judgment in its favour, Google is also asking for damages, attorney's fees, and an order enjoining the companies from further infringement of its patents.

The patents in the suit are US patents numbers 5,581,703 and 5,701,465 relating to "method and apparatus for reserving system resources to assure quality of service," 6,807,166 relating to a gateway for internet telephony, and 7,460,558 that deals with a system and method for connection capacity reassignment in a multi-tier data processing network. Three of the patents were initially assigned to IBM, while a fourth was assigned to Fujitsu, and appear to have been purchased later.

"We have always seen litigation as a last resort, and we work hard to avoid lawsuits," Google said. "But BT has brought several meritless patent claims against Google and our customers - and they've also been arming patent trolls. When faced with these kind of actions, we will defend ourselves."

BT's suit in December, 2011 in US District Court for the District of Delaware alleged that some Google products and services including Android, and its search, music, map, and location-based advertising infringe on one or more of six of its patents.