SwiftKey, a language tech firm, has secured £11.3m ($17.5m) in a series B round led by venture firm Index Ventures.

The London-based Cambridge startup is behind a keyboard app, also by the name of SwiftKey, which was the top-selling app on Android’s Google Play in 2012 and remains a bestseller on the mobile app market. The app was designed by two Cambridge alumni who found that smartphone users encountered difficulty in interacting with increasingly smaller on-screen keyboards.

SwiftKey’s app not only allows for a more intuitive word guessing facility on the keyboard, presenting three options based upon what the user has already input, but also includes a gliding feature which allows the user to quickly assemble words through a finger drag and click interface.

Other investors in the round include existing backer Octopus Investments and a number of angel investors, including angel investor Cambridge Capital Group.

Swiftkey has now raised $21.6m in venture backing. It received $1.25m in seed funding in 2010 from Octopus with a following venture round of $585k from the investor. Octopus also led a $2.4m venture round in 2011, which was joined by a number of angel investors.

Since founding in 2008, has grown rapidly and attracted licensing opportunities from smartphone developers such as Samsung. SwiftKey’s revenues grew five-fold year on year, and its headcount tripled in size to 100 staff in the past 12 months with new offices opening in Seoul and San Francisco as well as a new headquarters in London.

The company plans to use its latest round of funding to further develop its SwiftKey app, expanding its portfolio, and financing a major push into the US.

Jon Reynolds, chief executive at SwiftKey, said: “Smartphones and tablets are revolutionising the way we communicate – but there’s still so much potential for innovation and we’re determined to lead the transformation of this space. This major finance round enables us to aggressively pursue that vision, breaking new ground with our world-class language technology.”