Hi Dwardo,
I stumbled across a giant puffball whilst out walking along the banks of the River Mersey in Warrington during September. I picked it and took it home to consult my fungi reference books ( I dont want to go on about the book though) for a positive ID. It was the size of a football and like others have said, it is difficult to mistake with any other fungi or even a sheep. The main problem is it's state of ediblity.
The inner flesh should be white. I cut my specimen open to inspect the flesh which was white, Bingo! - so I cut half of it into slithers, fried it up with Bacon. Best shroom I have ever tasted. No wonder it is classed as one of the choice edibles. I kept the other half for another day.
The problem was In my experience, once picked it has a short shelf life of 2-3 days.
The white inner flesh started turning a yellow/green. I assumed it was on its way to becoming Black, by which time it would not be edible. But it was so good first time round, I thought I would take a chance. Mistake.
I cooked it as before but this time it had a bitter taste to it and I ended up with stomach ache for 24 hours.