When and in what context did Margaret Thatcher say that, "A man riding a bus (to work) at age 26 may count himself a failure"?

'A man who, beyond the age of 26, finds himself on a bus can count himself as a failure' (1986)
cited in Commons debates, 2003-07-02, col 407
http://en.wikiquote.org/wiki/Margaret_Thatcher

Misattributed to Margaret Thatcher according to the following explanation:

Attributed to her in Commons debates, 2003-07-02, column 407 and Commons debates, 2004-06-15 column 697. According to a letter to the Daily Telegraph by Alistair Cooke on 2 November 2006, this sentiment originated with Loelia Ponsonby, one of the wives of 2nd Duke of Westminster who said "Anybody seen in a bus over the age of 30 has been a failure in life". In a letter published the next day, also in the Daily Telegraph, Hugo Vickers claims Loelia Ponsonby admitted to him that she had borrowed it from Brian Howard. There is no solid evidence that Margaret Thatcher ever quoted this statement with approval, or indeed shared the sentiment.

https://en.wikiquote.org/wiki/Margaret_Thatcher#Misattributed