ATOS should not hold any of your information once they have assessed you and returned your case file to DWP.
When it comes to DWP, you should make a Subject Access Request to each department where you have a claim (ie, you should write separately for ESA, PIP etc).
Requesting a Subject Access Request (SAR) :
SAR Form Download From this page :
DWP Data Protection Policy Or you can make the request in the form of a letter, as long as you make it clear that you are making a formal SAR under The Data Protection Act 1998.
Address the envelope : FAO The Data Controller, at the Benefits Office dealing with your PIP.
Write DPA 1998 SAR in front, top, left corner of envelope.
Once received, they have 40 calendar days to comply.
Sending Documents to the DWP.