Twitter has announced its intention to acquire Tweetdeck, the London-based company whose software allows users to manage the microblogging service more effectively.

The deal, reported to worth $40 million, follows months of speculation and false alarms. Earlier this year, Tweetdeck was reported to have been acquired by UberMedia, a company that owned a number of other social media ‘clients’.

That was shortly followed by reports, from many of the same sources, that in fact Twitter was going to buy Tweetdeck. Now that deal is being widely reported, with CNN Money saying that papers finalising the deal were signed on Monday.

Tweetdeck uses Twitter’s application programming interface (API) to allow users to manage multiple accounts and to divide the people they follow into categories. It also allows them to view feeds across multiple social media platforms, including Facebook, LinkedIn and FourSquare.

Founded by Iain Dodsworth, a former programmer at insurance giant Prudential, Tweetdeck is the best known company to emerge from London’s Silicon Roundabout since last.fm. That company, a music-focused social network, was also acquired by a US company, broadcast giant CBS.

Besides this acquisition, Twitter is reported to be expanding its UK operations.