When did Aspirated Consonants appear in English?

Question

As stated here :

(in English) "The voiceless stops /p/, /t/, /k/ are typically aspirated when they begin a stressed syllable, becoming [pʰ], [tʰ], [kʰ] [...]"

Since these consonants weren't aspirated in Old English, I thought the aspiration would appear and be explained in a diachronic description of English, like this one. As far as I know, the explanation is missing.

Hence my questions : (1) How and when the aspiration appears ? (2) From when is the aspiration securely attested ?

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addendum : I read in Hogg's Cambridge History of the English Language (tome I, p. 89-90) :

"It is impossible to be more precise about the articulation of the [Old English] dental consonants [...] there is no way of telling whether these stops would have aspiration in initial position [...]"

Answer 1

This thesis by Bruin argues that aspiration is a feature of Old English, as also argued for Germanic in various places by Iverson & Salmons. Aspiration i.e. positive VOT is one of those under-reported phonetic details that is often ignored. For example, very few Bantu languages have an aspiration contrast and instead have a t/d voicing contrast, except that the voiceless stops are typically aspirated almost as much as in modern English. A widespread account of the ubiquity of aspiration fact is that aspiration "enhances" the contrast between voiced and voiceless consonants. Aspiration (long VOT lag) is so widespread in Germanic that it may be simpler to explain Dutch as an independent development than it is to explain multitudinous developments of aspiration (whereby Dutch would be a very conservative language).

Answer 2

I don't see how you reached the conclusion that Old English stops were unaspirated. Here is the most relevant reference I found:

"T" and "p" were possibly pronounced exactly like in Modern English "turn" and "police" respectively, but it is also possible that they were pronounced unaspirated - like in Modern Dutch.

from Old_English/Fōresprǣc. And see the rest of the quoted paragraph.