How to fill landing card for UK for back-to-back entries and exits?

My trip to UK will include three short visits of duration 4days, 7days and 2days each with a gap of four days in between each visit. I will be visiting Europe from UK during those two gaps of 4days. I have the following question to ask:

What should I write on landing card regarding my "Length of stay in UK"?

a. Should I write 4days at the time of first entry, 7days at second time and 2days at third time?

b. Should I write 13days (4+7+2) at the time of first entry, 9days (7+2) at second time and 2days at third time?

c. Should I write 21days (4+4+7+4+2) at the time of first entry, 13days (7+4+2) at second time and 2days at third time?

In my opinion, the option (b) seems to be correct.

customs-and-immigration multiple-entry

Best Answer

There's no option to "reuse" the landing card because you surrender it at the passport control. So no matter what you wrote there - 13 or 21, on your second entry you will have to fill up a different landing card, even if you only stayed 4 days.

Thus every time you enter UK you fill up a new landing card, and specify the new duration. Duration is the period until you leave the UK. Thus you will write 4 days on the time of first entry, then 7 days, then 2 days and so on.