UK social games publisher Playfish has announced that it's passed the 50 million registered players mark.

The company now has six games available on Facebook and other social networks - not bad progress considering that a year ago it had one game with 100,000 registered users.

Playfish, which was set up by several former staff from Glu Mobile's EMEA team, also recently passed the four million daily active players mark. 

In recent times, the company has taken its games from Facebook to MySpace, Bebo and Yahoo, fuelling its growth. It's also been hailed by the Financial Times and Edge magazine in recent weeks.

However, the question remains of when the company is going to try to transfer this success to iPhone and other mobile platforms.

When Playfish raised $17 million in funding last October, CEO Kristian Segerstrale (pictured) told PocketGamer.biz that mobile devices were very much on the company's agenda.

Its rivals in the social games space - including SGN and Zynga - have already launched their first iPhone games, so it's surely only a matter of time before Playfish follows suit.