Some of the smaller, and more common, sizes are much more prone to damage. You can often get away with it in the larger sizes, as you have proved, although as you are saying, it s not good practice. But 3/8", 7/16", 1/2" and 9/16", those that you access every time you work on a Mini, are not close enough to the nearest metric size and have a very high risk of damage.
To add to the misery of not having the correct tool sizes, some electrical items are likely to have BA threads and heads. Countries such as the USA are fully familiar with inch sizes, and increasingly, metric. Europe, almost exclusively metric, although those with older British vehicles or indeed any other British equipment will know about inch sizes. But who, outside the UK, has heard of BA?
On the other hand, I may be surprised because another ancient UK standard, BSP pipe threads, is in fact a worldwide standard for certain things. Indeed, it is the only standard for certain things. How that came about is one for the historians...
At least, with the exception of one thread form, not the hexagon, there are, as far as I have encountered, no BSW or BSF fixings on a Mini. Its predecessor the Moggy originally had quite a few.
