Dont need it!
Call HMRC ask for SA302 for the years you need 3-4 are normally enough, sign the form putting a note on there that your not an accountant, and post.
All mortgage companies prefer to have this SA302 and its a summary of the clients earnings and it shows what HMRC have on file for client. Which negates the use for an accountants certificate!!
And I've had 3-4 such requests, provided the SA302's and bamn! Mortgage accepted! thank you and goodnight! ;)