There have been further developments since my original blog post, on the topic of changes to TD Direct's client monies policy, which cause me to re-examine the issue and its implications.
Firstly, I am pleased that Interactive Investor, TD Direct's new owner, have responded to my post, as follows:
Interactive Investor’s primary responsibility is the security of a client’s data, cash and assets. Current FCA rules state that client money must not be placed out on unbreakable deposits of more than 30 days. ...