No major problems although contract changes imposed recently limit sickness pay. Personally I do not find this a problem although some colleagues were unhappy with the way this was done.
They pay you when you are ill. I have never not been paid.
Depending on your manager, you might get paid, you might not
Extended sick pay up to 6 months
Best thing: you get it. Worst thing: 5 instances in a rolling year and it's a meeting.
Sick days are treated as regular work days in terms of pay. There is a limit on the number of groups of days off you can take for sickness each year.
I haven't been away long enough in my time yet to see the benefits. You are paid the same amount if you are sick regardless. There may be a limit, after which you would need a note from a doctor. You get 27 paid holidays year across the business.