At my company, you have to be employed for a year before you get paid if off sick.  So if you have been here under a year and take a day off sick, you are stopped a day's pay, if you are off 2 days, then you are stopped 2 days and so on.

After a year, you can take 5 days self certification and be paid but after 5 days off, you need a doctor's note and then you are paid up to a maximum of 2 weeks.  If you are off for longer the company won't pay you but you can claim statutory sick pay which I believe is (or was) around £47 per day so probably a lot less than you actually are paid by your company.

I have gone to work when not feeling well as in a bad cold but dosed myself up to get through the day.  Co-workers then say that you should not bring your germs into work and I do agree but don't feel I can justify sitting at home all day with a cold. I only ever don't go in if I am unable to get out of bed with a fever for example or if I need to take regular trips to the bathroom  .