Analysis
Margaret Thatcher did remark during the 1989 Scottish Conservative Party Conference that resorting to personal attacks indicated a lack of substantive argument. However, the exact phrasing quoted – “I always cheer up immensely if an attack is particularly wounding because I think, well, if they attack one personally, it means they have not a single political argument left.” – does not appear in the official transcript and appears to be a paraphrase or embellishment.
Background
Thatcher was known for emphasizing that political debate should focus on policy rather than personal attacks. In her 1989 speech to the Scottish Conservatives, she warned that personal attacks signaled a failure to present a persuasive argument. Media reports at the time summarized this point in various ways, but none contain the exact quoted sentence.
Verdict summary
Thatcher expressed a similar idea about personal attacks, but the quoted wording is not a verbatim record of her 1989 speech.