In the case of Margrette Thatcher, I hear natives call her "Baroness Thatcher"
Likewise, can we call the Manchester Utd boss "Sir Ferguson" besides "Sir Alex Ferguson"?
Thanks for your help!
No. The titles of 'Sir' and 'Dame' are used before forenames only.
You won't hear many native speakers refer to the recently departed former prime minister as 'Baroness Thatcher'. Although it's correct, most people use 'Lady' rather than 'Baroness' and 'Lord' rather than 'Baron'.