I had one of these a few years ago and could never get to the bottom of what it was but believed it was a private purchase, so I'm pleased to see these examples, mine had the same chin strap and liner as Tinlids.

The shape is different, they are round and have circular tooling marks, based on this I think they are made by 'spinning' rather than being pressed, this process would be much cheaper than investing in tooling and would mean they could easily be made in a factory that made pots and pans. Ballistics wise they wouldn't be very useful.

Private purchse brodie/tommy helmet

The private purchase liner seems overkill, but who knows, if you have money to buy your own helmet in times of austerity, anything is possible.