Oxford West MP Layla Moran is currently second favourite in the party leadership race, although she has yet to confirm whether she is standing.
Antony Hook said the banner would 'send a strong message to the world that we still love Europe'.
Everything you need to know about the three major political parties' stances are on Brexit in the run-up to the general election.
Everything you need to know about Liberal Democrat leader Jo Swinson ahead of the General Election on December 12, 2019.
Leaflets claimed the data showed the Lib Dems neck-and-neck with the Conservative Party in Putney.
A "misleading" poll posted by the Lib Dems showed their candidate was polling just six points behind the Leader of the House.