BT plc officially cancel British Summer Time???

I have asked if this is their official position or not, and not had a reply, but they are doubling down on it...

Hi James,

We don't find any time difference for BST and UTC when we checked.

Please find the attached picture.

And they attached this...

This was all because they wanted a call at "5:30 BST" (not even stating AM/PM).

But wow, they are sticking to it. Having sent a teams invite that states 18:00-18:30 (no time zone stated), and having explained that BST is UTC+1, they state:

For tomorrow call has arranged for 6 PM BST

So, it seems BT plc have cancelled British Summer Time.

About time too...