OK , mingo
You need to review what you have already said to your ex employer.
You also need to decide what else you need to tell them without making it worse for yourself. For example you shouldnt need to incriminate yourself ( that is make admissions that have criminal significance NOT no admissions at all )
To a certain extent you need to think very carefully about how much MORE information you should give them. You have already admitted to taking it and passing it on
//Your letter with the undertakings, will also need to separately say exactly what you took, how, when and what you did with it.//
what you took - the 45 names and nothing else
how - direct access - sitting at a work terminal
when give the dates of your employment
and what you did with it - pass it to XYZ which the employer is already aware
what I said at the time I passed the info I cant recollect
what he did with it I have no idea
what he said he would do with it, cant recollect
Think about it ( the answer ) for a few days
and perhaps think about writing and not emailing
I think I have answered all your questions - I think there will come a time when you say I have admitted taking the data and passing it on, and you are not able to say what happened to it after that
It seems sensible to collect the data you say is already on the internet ( they wont ) as there may come a time when they say "this is very confidential and very bad" and you should put yourself in the position of saying - " well it is already in the public domain and so is not confidenti."al when the need arises
Remember the employer's lawyer is there to represent his rights and will not be concerned with yours at all.
at some time point or another even the employers lawyer is gonna say dont take it to court as we need our fee and the employee has no money so you are gonna have to pay in the mean time ,,,,
It is June - have you thought about three months holiiday in South Sudan or somewhere ? It strikes me you have made enough admissions and need a rest somewhere