Garth Marenghi's Darkplace: Garth's accent?

(A search of this forum revealed a very short thread from 5 years ago, which I didn’t think was worth zombifying.)

I just watched the series of “Garth Marenghi’s Darkplace” and I thought it was pretty funny.

One thing I was wondering: what sort of accent is Garth Marenghi supposed to have? It sounds somewhat distinctive, but I don’t know enough about British regional accents to place it to a particular area or social class or whatever.

Any conjectures? Here’s an obligatory Youtube link so you can hear it for yourself.

Youtube link is blocked on copyright grounds in the UK.

Don’t recognise the accent as a distinct regional accent, though.

He’s supposed to have grown up in Romford, North London, where he recovered from jaundice.

Hm, maybe it’s just me, then. I thought he almost sounded a bit Australian in bits.

Not even faintly. But funny as piss.

I was wondering if some of his pronunciation is intentionally off. For instance, I was struck by “author” when he introduced himself, which has a sound more like /t[sup]h[/sup]/ than /θ/. Around 1:00, when he says “ashamed” and “spacious” it sounds a bit strange as well.
“Naturellement” doesn’t seem quite right either. It could be that this is unrelated (since the mispronunciation of a French word is more likely to be done as a joke). Some other over-emphasis in his introduction, which doesn’t seem as noticeable in the intro to the ‘show’, seems to imply that he’s doing at least something intentional.

Specifically, when he says the word “day” (for example), it sounds a bit like “die” to me. Similarly “mutated placenta attacks Bristol” sounds like “mu-tie-ted placenter attacks Bristol”. Now if only I could get the Queen to say the same thing, so I could compare the two pronunciations…