siem Reap to Hong Kong - Visa requirements

Wouldn't the flight from Hong Kong to London qualify as proof of onward travel? Doubt you'll be asked though.

No I don't think. I was never asked last time I was there.
And you HK ticket does constitute as onward travel.

I don't really understand the question either. If you already have your HKG-London ticket then what's the problem. You have your proof of onward travel if asked.

As to whether you will need it, there is a slim chance that the airline will require one. The airline's excuse is always that they need to cover themselves incase you are refused entry into the destination.

If you are waiting until you get to HK before buying your London ticket, remember that usually the closer you buy to when you fly, the higher you pay. Online one way tickets can be bought from Oasis.

op, you will be fine. brits still get 6 months visa-free upon entry to hong kong as far as i know

Immigration in Hong Kong is not the problem for the OP, it's the airline allowing him onboard with a one way ticket. True it should not be a problem, but the worse case scenario would see Siem Reap Airlines making you buy a ticket with them out of Hong Kong.

Thanks for the useful replys,

#1 I havn't yet brought an onward ticket yet as im waiting for money, but have to leave Cambodia for visa reasons. - heading to Hong Kong to take advantage of Oasis Airlines cheap flights. (yay!)

will chance it and let you know the outcome. (fingers crossed!!)