In October, I emailed the London Mayor to oppose a permanent split between the Bank and Charing Cross branches of the Northern Line, which had been mooted. I have received an email from the General Manager of the Northern Line in response. I have replied with some further queries, as it still appears that Transport for London could be planning to split the branches at certain non-peak times of the day - a really bad idea.
At the moment, you can get trains in and out of town on the Edgware branch via either Bank or Charing Cross. If the line was split so that all Edgware trains were via Bank at certain times of the day, you'd ALWAYS have to change trains at Camden Town to get a Charing Cross train at those times of the day, which would cause great inconvenience to regular passengers. The same would be true if all Edgware trains were via Charing Cross, which could also happen if the line was permanently split - either way, I think it is a really bad idea.