Actually TightSlot, Cabin Crew UK employees, even though based in the UK, operate on VH (Aussie) registered aircraft, therefore come under CASA (Aussie) rules regarding everything, including Flight Limitations. Thats why they can get away with rostering CCUK crew up to 240hrs in a two month roster.
As CASA doesnt have much in concrete about Flight Duty Limits for cabin crew, it would depend on what is in the local contract there is in regards to multi-sector flight limits. Aussie based crew couldnt do a 17hr mutli sector day (the limit here is 14 hrs planned duty for a multi sector day...but thats only in our contract/EBA...nothing to do with CASA).
So basically, if it's within their contract limits they can do it. Although I am sure their union would have something to say about it.
I'm not too sure what their current contract says about multisector duties.