If anyone's interested: The German site election.de did a "What if UK had used the German election system?" scenario (= you need at least 5% of the vote or three constituencies to be included in proportional seat allocation).
The results:
http://www.election.de/cgi-bin/tab.pl?datafile=uk2010_szenario.txtTories 257 (difference to actual result: -49)
Labour 206 (-52)
LibDems 164 (+107)
SNP 12 (+6)
DUP 4 (-4)
Other parties 7
Of course, it comes down to a Tory/LibDem or Labour/LibDem coalition again, just with much stronger LibDems.
Note: For the purposes of the scenario, the number of British constituencies was apparently cut in half, since only half of the MPs would be directly elected.
