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They have face value - the fact that this face value is not clearly stated on them is another story. But those coins have legal tender status and are officially worth 25 pence each :-)

BTW I suggest to use tag #numismatics not #numismatic - first one is much more popular and has correct spelling...

Those more modern "crowns" worth 5 pounds have face value written on them.

You my friend are full, of useful information! Thank you i have edited the tags :)

Run few more queries - if you want to be sure get the coin checked because there are fairly good quality fakes available from Chinese distributor: https://www.aliexpress.com/item/United-Kingdom-Coins-1928-CROWN-Britain-Copy-Coin-Copper-Silver-Plated-CEORGIVS-V-DEI-GRA-BRITT/32818779249.html for less than $2 and if they are made from copper then magnet would not help as copper is non-magnetic.

How can i check its authenticity?

Well, as somebody mentioned it earlier - check the weight. Or better find a local coin dealer.