How many new episodes per season for American TV? and per series for British?

Once upon a time, American television shows used to produce 39 new episodes per year (per TV season) and then rebroadcast the best 13 over the summer (“summer reruns”), making a full 52 weekly shows—a year’s worth. Then the new season would start in the fall. This was long before VCRs, so most of the season’s shows were seen once only.

It’s been so long since I watched American TV that I have no idea how many new episodes appear in a season (a year’s worth), but I know is hasn’t been 39 or probably even 26 in years. How many is it? What’s a season’s full count of shows for an ongoing American television series?

The BBC shows and other British television programs I watch on Netflix typically have only about 8 new shows in a series (season). Is this standard? Are they shown over and over, or do different shows have their series run at different times of year, or are the episodes spaced out over months instead of week by week, or what? Is every British TV show basically just a miniseries—a few weeks’ worth, and then that’s it until next year?