I have worked at M&S for ten years. The absence policy allows for 8 periods of absence in a 26 week rolling period. A period of absence is the time you have off without returning to work, so if you took two days off, went back for one day then took another two days off that would be two periods of absence whereas if you took the whole five days off that would only be one.
You are expected to call every day of your period of absence. If you are off for more than 7 days you will require an unfit to work note from a Doctor and will have an agreed level to of contact with your manager but are not expected to call every day. Long term sickness absence does not count towards a trigger and neither does absence due to a known long term health condition (this means known by the business, not just known by you).
If you do trigger you will be invited to meeting with your line manager to discuss your unacceptable level of absence, for this you may receive a warning, this does not mean that they believed your illness was not genuine. The warning will stay on your record for 12 months and your absence allowance will reduce to six periods of absence in a 26 week rolling period while your warning is live.