The coin pictured is a smaller version of the one-tael coin produced by the Hong Kong mint as a proposed China trade coin. It was rejected by China, possibly because it carried the British royal coat of arms.
The coin shown is 39.2mm diameter and weighs 25.3g. Beneath the royal atms on the reverse are the figures 982 - presumably silver purity - and g 366 - weight.
While this is plainly not a genuine coin, it is very well made and interesting.
More detail can be found on the Xeno.ru database, ref10634
This should be listed under 'China',not 'Hong Kong'.