-Laughs Uproariously- Great letter that conveys his feelings clearly without rampant emotion clouding the message. Mind you, there's clearly plenty under the sarcasm. I might have said "...only home I have ever known." rather than "...only place I have ever known." but that's a nitpick and does not detract from the letter one whit.
Now, I could see this as a prequel to a story where the Dark Lord Marik is as stupid as the Ministry and attacks Harry and/or his lover and the UK finds out why ticking him off really isn't a good idea, period. I could easily see it as the prologue to a story similar to Kinsfire's "Burning Day" and with roughly the same outcome.
I had actually put "... the only home" first, but I changed it. I'm glad that you liked the story.