Can meditation cause you to sleep less?

Over the last few months I've started meditating late on a night (as well as my usual morning practice). I'm finding that I am sleeping less but not feeling tired because of it. Is there any information around about how mediation may or may not affect sleep patterns? For instance Dipa Ma , the Indian housewife and meditation teacher was up at 4.00 am every morning to meditate for a few hours presumably finding that perfectly OK. That said Margaret Thatcher only slept for 4 hours a night and I would hesitate to call her a Buddhist meditation master.