Matron's jotters

I have to admit I had never heard this expression until a foreign bike trip when John would arrive for breakfast each morning and declare " thats me in Matron's jotters". What are you talking about?

The explanation was that whilst at boarding school, Matron would ask all the young boys each morning if they had managed a bowel movement. Those who had were ticked off in "Matron's jotters". Those that hadn't were given cod liver oil.

My good lady and I now use the expression daily so as to politely advise the availability of the toilet.

This morning, we are both in Matron's jotters!!