The title of baronet, which has medieval origins, identified by the prefix Sir to Christian and surname, is a hereditary honour descending from father to son. It is not a rank of the British peerage.
A wife of a Baronet has the style Lady before her surname. A husband of a Baronet does not derive any style from their husband.
Formally addressed as ‘Sir James’ and referred to as ‘Sir James Robertson’. The same rules apply for knights.
Sir
I have the honour to remain your obedient servant,
Envelope: Sir James Robertson, Bt
Madam
I have the honour to be Your Ladyship’s obedient servant,
Envelope: Lady Robertson
Dear Sir
Yours faithfully
Envelope: Sir James Robertson, Bt
Madam
Yours faithfully
Envelope: Lady Robertson
Dear Sir James,
Yours sincerely
Envelope: Sir James Robertson, Bt
Dear Lady Robinson
Yours sincerely
Envelope: Lady Robertson
Baronet is shorted to Bt but the more old fashioned was Bart. Either is fine but Bt is more widely known.
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