My 02 plate
first started to show these symptoms at about 30K miles. Then it was a slightly lumpy idle (regular beat). Used injector cleaner every 5th tank and now at 45K miles this has become more erratic rather than lumpy.
It's now only just noticeable (nothing like yours it seems).
Reading the various threads here suggest many possible causes from imbalance compression through fuel pressure problems, injector faults etc. Since your problem seems to have got much worse over relatively few miles I can't see that this is compression related.
I have one other possible cause - battery problems.
I recently had to replace my battery due to problems starting. Before this I noticed that my dash illuminmation would flicker when the engine was at low idle. With the new battery (75Ah!) that's gone and I'm sure the erratic idle is better.
My reasoning - the injectors are driven directly from the 12V supply. If the voltage is modulated at low idle (from 13 to 15Volts) then the response speed of the injectors will also vary. The fuel gets to the plug a little bit late and power output is reduced. The
engine is heavily relient on accurate timing of the inject and the spark.
Just a thought.