**Answer** Your bottom bracket is stuffed.
The cheap AND the correct fix is to replace it outright. All I found on the web was that this bike has an "external bearing system" bottom bracket, which could be any of 9 different standards.
The replacement has to match the crank interface too, which could be ISIS, Octalink, or square taper.
![Misc one from Wiggle's site](
Specialised tools for this - you might need a crank extractor, which forces the two crank arms off the bottom bracket spindle. Then you need a special wrench to undo the visible round bits poking out the side. They may be threadded or they may be pressed in.
Lastly you may require a press to push the two halves together or you may get away with using the special wrench to thread them back in.
You'll also need grease or copperslip, and standard workshop tools.
Would be cheaper to get a LBS to do this if you don't own or want to own the tools. And a BB should last you at least 10,000 km.