Shifting the policies of European nations even further to the left in the late seventies and the beginning of the eighties seems to require the following ingredients:
An alternative to Keynesian policies that involve the increase of income to beat inflation. This type of policy, intended to prevent a repetition of the crisis of the thirties, is basically bankrupt at this time. Maybe a type of policy that corresponds to corporatism becomes a reasonable alternative to the left, although it will be hard imagining the left switching over to a corporatist, confessional political structure and landscape.
Getting rid of the inertia that seems inherent to the leftist parties at the time. Many of these parties as far as I can see seem almost dogmatic in their confidence in Keynesian policies to solve economic issues. You need some kind of nineties, New Labour/ third way alternative available at PoD.
A new kind of consensus between the unions and the government, in which the unions no longer demand full employment. Maybe, in exchange, the unions get to represent the interests of the unemployed as well, on the one hand securing their welfare, on the other hand negotiating with the government for the means for re-education.
The IMF is mentioned as an organization enforcing or at least encouraging monetarist policy. Maybe the European Community becomes the podium for at least the Continental leftist parties to formulate and execute an economic counter to the problems of inflation, fitting maybe within the framework of European federalism...
Just a few ideas, hope that it helps.