Comment by rsynnott

From the point of view of the manufacturers, the Single Market is, ah, a single market; they only have to get type approval once, and then they can sell anywhere. The only real complicating factor is Ireland and Malta, which drive on the left side of the road (and some niche cars will never be released there as a consequence; for instance Tesla stopped selling Model S/X in a left hand drive configuration a while back, though they now seem to have stopped selling both in Europe entirely, in any case).

Post-Brexit, the UK has its own type certification (and of course it also has the left hand drive problem), and, again, some niche car models may be available in the EU but not the UK. But in practice, for mainstream stuff, the manufacturers tend to treat it as just part of the European market.