Ich war schon am Loch Ness und am Loch Lomond, dazu noch auf etlichen Pub-Singalongs mit den Bonnie Bonnie Banks of Loch Lomond etc..., also: ich habe lange in Schottland gelebt, und da habe ich das "och" nur ausgesprochen wie in doch gehört, nicht wie Dock.

Ich könnte mir vorstellen, dass nicht-schottische Briten Schwierigkeiten mit der ch-Aussprache haben und eine der in #0 genannten Aussprachevarianten als Ersatzaussprache heranziehen.

Ja, Reisen bildet. Neulich war ich im Alten Land - war auch schön. :-)
Ob man mal den anderen Lexikographen eine Reise in die Highlands nahelegen sollte?

Spinatwachtel is right; I heard and said "loch" (wie doch) before leaving the UK (SE England); in the meantime my German is pretty good so I can pronounce it even better. :-)

I saw your subject line and thought: easy peasy, same Aussprache as in German.

But then I imagined myself saying it, and indeed I doubt I would actually say Loch Ness in conversation with fellow Engländer. I'd be more likely to say Lock Ness, Lock Lomond, just because it's easier. It might sound a touch pedantic to always pronounce the 'ch' sound outside of Scotland, a bit like insisting on the 'th' in chorizo.

So my conclusion is that most Engländer would know it has a 'ch' sound, but probably just pronounce it 'ck' for convenience. Perhaps.

Being from Northern Ireland I agree with #1 and #2. The correct pronunciation of loch in Scotland and lough in Ireland has the same ch sound as in German Loch.
However, English speakers frequently have difficulty with this sound so it sounds like "ck". Thus they have the same difficulty with German "ch". The vowel sound of the o is also slightly longer, so for me it doesn't rhyme exactly with Loch or doch but it is pretty close.

it sounds like "ck".  

as in "Sprecken See Inglish?" ;-)