Thanks for the info
@Harry Bloomfield I didn't see it earlier, no new post email prompt from the forum.

I will hoist the dishwasher pipe up as you say.
I thought I'd update as we've since experienced the drain water coming through again! Only once, but it's enough to make me wary something is still not right. We're also experiencing oddities with the machine's spin/drain function working only intermittently. In case this is also related to the drain, I thought I should investigate more.
I've attached the page from the manual which describes the proper setup of the machine according to AEG. The other image is how I've got the hoses setup currently.
Some questions,
1) Could my current hose setup still be at fault? Given the heights and hose contortions? Note that my sink drain spigot is slightly below AEG's recommended minimum height.
2) Because the washing machine's sink spigot will naturally draw sink drain water down into it, because of it flowing downwards would it be better to swap it with the spigot the dishwasher is currently occupying?
3) Regarding the drain possibly causing an issue with the machine's spin/drain only function. Since both functions are tied together, could the machine be experiencing issues pumping out water? Or at least not enough to tell the machine, 'ok, you can now spin'. The symptom is that the machine just keeps gurlging away draining, then the spin starts but doesn't get up to speed, then cuts out and the process is repeated several times before stopping?
If anyone could advise on this I'd really appreciate it!