The Evening Standard report that "firefighters were called to the station after smoke began billowing from singed bread left unattended in a toaster — once at 8am breakfast time and the other at 6pm tea time."
This was confirmed by a TfL spokesperson who said closures on March 13th and April 7th were caused by "smoke from a toaster in the staff area of the station. London Underground has extensive heat and smoke detection systems, fire alarms and sprinkler systems and both alerts were dealt with quickly."
Apparently, burnt food in staff kitchen also led to a closure at Caledonian Road Tube station on the Piccadilly line earlier this year.
The official report concluded: "Upon inspection of room found the cause of smoke, someone had decided it was a good idea to store their box of Rice Krispies and four custard cream biscuits in the oven."
Perhaps there ought to be a new kitchen Inspector just for these incidents, like Inspector Sands who is called for when a fire alarm has been set off. If you hear "Could Inspector Ramsey or Inspector Oliver make his way to the control room", you'll know that settings on the staff toaster need adjusting.