Your letter is fine but I'd suggest a heading in bold and underlined;(posted 8116 days ago)"Request For Assessment Under The Data Protection Act" ------------------------------------------------------
I also complete my assessment letters to the IC with the statement;
Please investigate and issue an assessment. -------------------------------------------
So that there can be no misunderstanding by the office of the IC. You might also consider completing an assessment form which is available for downloading on the IC website.
Good Luck.