As a retired IT consultant, surely you realise that if BT didn't operate a spam filter at all you would be inundated with thousands of spam emails daily.
There is not a 'current fault' , the BT spam filters have been broken for years. They lurch between being overly aggressive and too lax.
@Rick1948wrote:Changing email provider is hardly a simple fix when, as you state, it would take several months to effect, and who is to say that gmail is going to be any better, long term. I have been with BTinternet for many years and do not wish to change from what in many ways is a good service, simply because there is currently a fault with its spam filtering. The "simple fix" is for BT to revert to providing users with the option not to use the BT spam filter, like they used to. As a retired IT consultant, I would happily assist them in this at no charge.
Several months is going to be easy to manage. Similarly if you change ISP, you will then not be tied to BTinternet email addresses either browser access or paid for premium.
The only fault is BTinternet email.