Now for external walls. What's the best material. We need to consider:
1) Cost
2) Appearance
3) Maintenance
4) Thermal performance (they're all the same)
5) Durability
Since the Georgian is look is all the rage why not rendered aerated concrete walls. More insulation than clay brick, less embodied energy and lighter and faster to erect than laying masonry.
The insulation value of clay brick is neglible, all its thermal properties are related to thermal mass (and that is best kept inside the house)
Rendered aerated concrete walls need to be painted every 10 years. Add the need for regular exercise, daily flossing, working, showering, cleaning the house, buying the groceries, laundry, cooking, washing up ... I won't have the time!