Margaret Christian "Peggy" Jay (4 January 1913 – 21 January 2008) was an English Labour councillor.
As a young girl, Peggy Garnett attended St Paul's Girls' School in London, where she befriended Shiela Grant Duff.
She went up to Somerville College, Oxford in 1931, but left two years later to marry Douglas Jay.
Joining the Labour Party, she was recruited by Herbert Morrison to be a candidate for the London County Council (LCC); from 1934, she represented Hackney South, then Battersea South, and finally Battersea North.
Later, she was elected to the new Greater London Council before losing her seat in 1967.She left the Labour Party in 1981 for the newly formed Social Democratic Party, not returning until shortly before her death.
She was the last survivor of the "Hampstead middle-class Labour grandes dames" whom Morrison had groomed to take over the LCC.