We have a chest freezer in a cupboard under the stairs.
It is crammed full of frozen food.
At about 4pm yesterday, I took something out of the freezer, leaving the lid open at about 45% and shut the cupboard door.
At about 5am this morning I opened the cupboard door, discovering that the freezer had been open all night.
Is my food still okay ?

Some at the bottom might be. Difficult to say. I'd err on the side of caution. Happened to me once...had to cook the entire contents of our freezer the next day!

Well some of the food at the top might have defrosted a little bit. But what happens is that the frezzer will go into overtime trying to keep everything at -18.

So my food is ok ?
When I found the freezer lid open this morning, I just shut it again !
Hope nothing has "gone off"

Someone told me once that frozen food starts to defrost after 5 hours, not sure if it's 100 percent true though.

I've done this before (door hasn't shut properly and not noticed for 12 hours or so). I have found that the ice-cream, bread and chips has defrosted but the meat at the bottom, if I have a feel, is still completely fozen solid.

I know this also form when our freezer broke down and we couldn't get another one for a couple of days. The processed meat defrosted immediatly, but cuts of meat stayed frozen a lot longer.

But not if its still in the freezer with the door open....