soit qui mal token britain?

2.77 grams and 20 mm
It's exactly like this but without the year:
http://www.omnicoin.com/coins/965926.jpg
what is it? is it on numista?

Anyone?

 Without looking it up anywhere, I think it is play money.

It looks really old

 Yes - probably around 1850 give or take 10 or 20 years - until someone can find more information.
I have seen similar, and may have one like it somewhere - it is a Victorian version of the modern Monopoly money, in a way. They were different sizes and sometimes with denominations on, and people used them when playing cards, rather than gambling with real money.

Is it on numista?

 Not sure yet, and 'Honi Soit Qui Mal Y Pense' is the motto of the Prince of Wales, with the three feathers being his emblem.
 I have seen it being described (on a token also undated) as a model half sovereign, size 19mm, and made of brass. From early to mid 1840's.  

 A little like, though not the same as, this item ...
https://en.numista.com/catalogue/pieces56768.html
 but it shows the area it should be entered in.
 I would list it as
Overse: Portrait left, no date below
 Lettering: VICTORIA QUEEN OF GREAT BRIT:
Reverse: Three feathers (the Prince of Wales plumes) within a crown, surrounded by the motto of the Most Noble Order of the Garter
 Lettering: HONI SOIT QUI MAL Y PENSE