Be careful about reading too much into that - "Large enterprises, those with 250 or greater employment, accounted for only 0.4 per cent of all enterprises." according to the ONS. You'd expect to see 89.4% small companies by chance alone, although I concede that if a company is around for 100 years you might expect it to grow into a large company by inertia alone.

With respect to your other point, you are absolutely right - I wanted to show my working here to indicate how badly wrong back-of-the-envelope calculations can go in situations like this.