Andreas Murr and his team correctly predicted on the 4th of December a big majority for the Conservatives.

His approach based on "citizen forecasts" ranks 2nd for the Conservatives and 5th for Labour in terms of accuracy among 19 pre-election seat forecasts. You can read more about his forecast on the LSE British Politics and Policy blog and about the other 18 forecasts on Steve Fisher's Electionsetc blog.