I hope you dont mind me posting but I work in Health & Safety so I know the law and i can 100% say you have a case to sue for negligence, both the hospital for misreading your smear and your GP for not refering you for a colposcopy as there is no way from a visual inspection they could tell it was cervical erosion.
I know this as i am suing myself for the same thing. Clear Smear in Jan 2012, Abnormal bleeding April 2012 which GP said was nothing. Smear in March 2013 showed 7cm tumour on cervix.
I have found myself a brilliant lawyer in London called Field Fisher and they have taken my case on.
No I understand that not everyone is the same and some feel differently about this but i have Stage 4 cancer which if diagnosed a year earlier would have been a Stage 1 so i am angry. No one can tell you what to do my lovely but i just wanted to say that from what you say and what i know of the law it may be something you may wish to persue if you feel like you want too.