Very interesting
Here in Ireland (just right beside the UK) we have the daylight savings as well. On June 21st is the Summer Solstice which is the longest day of the year where the Sun can be out. Iv seen the Sun stay out until 11pm at around this time.
Downside is that we lose time further on during the year when it comes into winter and it is not suprising for it to be bright until 10am and then dark again on the same day at 3pm.
It was interesting to know that Japan doesn't have this system. I know i always use to get confused or even panic sometimes when it came to the changing times (as in waking up and thinking i might be late for work or missed my bus etc)