It does look like an Aussie raw edge lid. Dont recognise the flash.
I automatically wrote British, without a second thought. Of course, it is quite possibly one of our antipodean allies helmets!
Nice relic of British MkI*.
Doesn't look like any Australian unit I recognise and Australians only very rarely painted unit patches on there helmets.
The chinstrap fasteners are also bent the wrong way to be any australian helmet.
Maybe the rim has came off in some point in the past?
Interesting helmet, good luck with investigating it further !!
It could be a kiwi unit??
As Piotrek said a British Mk1*. What colours are the flash?
the flash is a cream/pale yellow and black colour as per photos 2 and 3.
Whatever it is, it's a nice and gritty example