Hi Barry Sheen,
Unfortunately I believe you cannot see any specific computations and I also believe you are advised when submitting the details to keep a copy as you will not be able to view them online.
We can of course provide you with copies of assessments we have issued, or we can issue you a copy of the computations we have received online.
And you can view your accounts at Companies House.
I would also advise you contact 0300 200 3600 which is our online service helpdesk if you require assistance.
Technical support with HMRC online services
Thank you.