This may be a factor of the insulation standards of the average house in the area. Heat pumps require a high standard of insulation otherwise heat loss would cancel out a fair degree of the heating efficiency. You'd generally find insulation standards in Nordic regions to be of a very high standard for obvious reasons.Having emailed 3 companies in my area they now all confirm in Scotland the recommendation is an ASHP backed by a hydrogen ready gas boiler to boost the temperature. I can only go by the advice and recommendations of the companies fitting the systems, I have limited knowledge but my brother who designs AC and Heat Pumps has that exact set up in his house.
I will look into the Scandinavian model as we are clearly being wrongly advised in the UK