Newbie with emissions warning symbol

Hi all,

from an A4 to a 2007 A6 2.0 Diesel that I have had since 2010.

Working from home and the car doesn't get used that often... (once a week) no motorway driving but every week or so dual carriageway 60-70 mph for 15-30 miles - 95,000 miles on the clock.

From being parked for a few days - got in and the engine emission warning symbol came on. - I thought that driving for 20 minutes + at revs over 2000 this might fix this.. but no it didn't.

My questions are -
1) how come this light came on at start up?
and
2) I don't have a lot of money at the moment and cannot take the car to a garage for a couple of months - could this possibly affect any problem and make it worse? (and not driving the car)