Analysis of information sources in references of the Wikipedia article "Peerages in the United Kingdom" in English language version.
When a lady is divorced she loses any precedence which she gained by marriage. With regard to divorced Peeresses, the College of Arms, acting on an opinion of the Lord Chancellor, has long held that such persons cannot claim the privileges or status of Peeresses which they derived from their husbands
If a marriage between a duke and a duchess has been dissolved, the former wife (although no longer a peeress) may continue to use her title as a duke's wife, preceded by her forename (unless she remarries)
The correct style and description of divorced ladies who have not remarried nor have taken steps to resume their maiden name with the prefix of Mrs, is as follows: The former wife of a Peer or courtesy Peer,——Mary, Viscountess——
if she remarries, she would take the style of her subsequent husband...if Tessa, Viscountess Tilney, marries Mr George Robinson she becomes Mrs George Robinson
{{cite web}}: CS1 maint: multiple names: authors list (link)2 — Section 1 shall not apply in relation to anyone excepted from it by or in accordance with Standing Orders of the House.
{{cite web}}: CS1 maint: multiple names: authors list (link)