At Fish & Cook on Blackstock Road I buy three fine liner pens - pink, purple and green.

"Strange colour scheme, there" says the stationer. He often feels the need to comment on my purchases.

"Doing notes and referencing," I say.

"In purple?"

I want to say to him "Why do you have purple pens if you are uncomfortable about people buying them?" but I just smile.

The coloured pens are actually a trap to prove to my kids that they are always stealing my fine liner pens, but that is too complicated to explain.