Party at home : no need for a search warrant?

A Taiwanese friend of mine had a very unpleasant surprise a few days ago : he received a notification from the tribunal about something that had happened 2 years ago…
in 2001, he had a small party at home with two friends, they got high and/or drunk, probably got a bit louder than reasonable, and one of the neighbours must have called the police. The police came in, searched the guests and the appartment, and found 3 pills of Ecstasy on the table… My friend did not think much, and admitted they were theirs.
Of course, they took everybody in for tests, and the three of them tested positive for MDMA. At that time, they served a month in jail, and thought they were done with it…
…until a few day ago, when this friend was notified that one of the pills they had found contains something else than E, probably more serious.

Which leads to my question :
does the police have a right to burst into a private property without a search warrant ?
If this happens, can you oppose to them stepping in ?

And to extend the question a bit :
does that not apply to raids in discos and bars too ?
There seems to be an awrfull lot of them recently…

Connie L.
better safe than sorry