The problem is that you are trying to get compatibility between two different scales, with both modelled to an accurate gauge for the scale. Not possible, and somewhere along the way, you have no choice but to compromise. That said, you do have a variety of options, some of which you have noted, but there are also some others. I suggest you consider the following possibilities:
1) Separate layouts, each modelled to the correct scale:gauge ratio;
2) Use Proto:48 track and wheel standards, but have your UK models built otherwise to 7mm scale;
3) Forsake the existing British market, and model exclusively to Proto:48 develop your own 1:48 range of components, etc;
4) Forsake the US market, and build everything to 7mm scale and S7 standards.
Option 1 would require storage space, but is probably the easiest. Option 2 is very workable, but you will lose out on the ability to run your 7mm stock on S7 or indeed 0 gauge layouts. Options 3 and 4 are mentioned in case you want a real challenge!
Forget that 1:43.5 and 1:48 are both called 0 gauge, and start from the premise that they are different enough to require a separate approach. See if you can accept that approach, and the consequences of it (two layouts) and if not, consider other alternatives and more importantly, what you want to achieve.
As a more exaggerated example, you wouldn't try to run Proto:87 and P4 on the same layout, and if you mix 1:32, 1:30.5 and 1:29 on 45mm track, the visual results can be awful.