Yeah, I accept that some individual items to achieve passive are expensive, but I'm thinking that;- The benefits achieved from the building as a whole will be geater than the individual parts & The value of the building will be enhanced by the passive acreditation. Denby Dale / Green building store passive houses seem to be cost effective overall. But I'm also aware of critisims of the cost effectiveness of passive standards.
Agree entirely about air permeability and as mentioned previously I'm planning breathable walls comprising Brick outter skin, air gap, breathable membrane, rock wool insulation, block inner walls & lime plaster.