What always strikes me is that in the UK (well England more than NI) what is called "middle class" is not 25-75% income percentile...it is more top 25% and sometimes top 10%.
Isn't middle class in GB the bigger percentage? To my mind lower-middle to upper-middle encompasses a pretty broad range of professional, specialist and retail services. But I guess it all depends on how you define it. Big house, small house, flat, owning, renting - I don't think any of those conditions excludes middle class. On the other hand if being working class means not having assets, then maybe you can't be middle class and not own property.
We have to redefine things though - eg education qualifications like A-levels and degrees used to be a signifier of middle class, but if half the younger population has them, it doesn't give you significantly more security, so are they really useful signifiers anymore?