The Android operating system continues to take over the world, with a new report from The Guardian estimating just short of half the smartphones in the UK are running on Google’s operating system.

The Guardian reports that half the population of the UK owns a smartphone today, and in just 18 months half those smartphones have become Android phones, according to Kantar Worldpanel ComTech. By comparison, Apple’s iPhone holds 18.5 percent of the smartphone market, while Research In Motion’s BlackBerry accounts for 22.5 percent and Nokia’s Symbian has fallen to around 6 percent. It’s a sharp decline for Nokia, which held 20 percent of the market a year ago. Apple’s share also fell pretty drastically, down from 33 percent last year. Those numbers don’t include the recent iPhone 4S sales, though, and are somewhat in line with the decline in sales Apple saw worldwide with the run-up to the release of its new handset.

The number of smartphones being sold in the UK is accelerating, and in fact the entire worldwide market is growing pretty rapidly. The Guardian report states that it’s likely the UK will see 90 percent smartphone ownership within the next two years, as carriers move away from feature phones that make them less money both through sales and data contracts. In the 12 weeks ending on Oct. 2, smartphones made up about 70 percent of all cellular phone sales in the UK.

The Guardian expects Android’s share of smartphones sold in the UK to continue to rise as Android takes control of the lower end of the market, selling phones made cheaply in China that will cost users almost nothing up front and will help the operating system to really grow. The expectation is that, on the backs of cheaper phones, Android could expand its hold on the market to as much as 70 percent. Meanwhile, Apple’s iPhone can’t stay ahead, largely because of its premium price.

Kantar also noted that among Android smartphone makers, HTC is in the lead in the UK with 45 of the sales during the last quarter. Samsung, the world-leading smartphone seller, is in second place and catching up fast with 38 percent of Android sales. Meanwhile, Sony Ericsson’s share of Android sales dropped from 20.5 percent a year ago to 8.5 during the last quarter.

Kantar expects the next year to be an interesting one among Android manufacturers and carriers in the UK as lots of customers come to the end of two-year contracts and become eligible for upgrades. There will be plenty of vying for customers among all the companies, the firm expects, but it believes most customers will remain loyal to Android, about 62 percent. But loyalty among handset manufacturers is a lot lower, so it should an interesting year.