Toilets including those at Pond Square in Highgate, South End Green and West End Lane in West Hampstead, and Russell Square in Bloomsbury are all set to go. The automated toilets at Lincoln's Inn Fields - London's largest public square - and Camden Town are also to become user-pays.
Locals pointed out the decision follows Camden Council's decision to introduce a "wee fee" of £100 for anyone caught urinating in public.
Overall the closures and entry fees will save the council £250,000.
Local pubs and bars will be invited to open their toilets to the public in exchange for the council paying cleaning costs.
Dame Joan told the Camden New Journal she had received many letters from older men and women concerned that the loss of public toilets would affect how far they could venture from home.
She said: "It's the older people that have the weak bladders and they don't like to say so."
When the plans were first reported in November local councillor Julian Fulbrook warned the changes would see homeless people defecating in Lincoln's Inn Fields as they would not have the 20p needed to gain entry to the toilets.
Public toilets in Cardiff and West Berkshire are also on the chopping board as part of councils' budget savings plans.