Half Penny 1943 struck on a thin flan.

[$and€r]

Another one which I'm not sure if it is a genuine piece..
Please let me know what you think about this one.. 

weight: 2,2 gram
diameter: 24,5mm

(N# 870)

[Offa]

My first inkling would be to say fake.

[FosseWay]

I suspect it's real but has undergone "aftermarket modification" as they say in my industry. Namely, in this case, some quality time in something corrosive, like sulphuric acid.

[Mister T]

Agreed that it's probably had a bath in acid.