Small White Butterfly

What is a Small White butterfly doing flying around my kitchen in October?

It has been very mild but I wouldn't expect to see this around at this time of year. It took a great deal of interest in my mobile, probably my use of sticky fingers, and kept landing on it when the screen was on.  

Note the crack in the screen, courtesy of butterfingers. I should repair it but it's just superficial.  

Not the most interesting of shots but all I have to offer from today.