I have now tested a method of making my bike compliant with the 200 watt requirement. On power up the bike comes on in Mid Mode. By fixing a cover over the two mode change buttons (permanently held in place by means of glue or by other means) the operator no longer has access to either the High or Low power Modes.
I have not got a current meter in place at the moment, but based on previous experience and also on observations of the battery voltage drop when pedaling hard against a high resistance, I am pretty sure that the maximum power in Mid is around 60% of the power in High. By this means I should be comfortably bringing the En15194 tested 250 watts below the 1983 EAPC's 200 watts.
It is a pity that I shall lose access to the Low mode, but the range of the bike is so good that I can live with Mid mode. I will just get a bit less exercise. I shall miss the High mode which is so useful for the very steepest of hills, but nearly everything I encounter can be done slowly with Mid assist. I just have to accept this in order to assure full legality.
Oh, yes, I will also need to get a plate made up giving voltage and power.