Weight should be 5.69 (Krause), Silver is 5.43. the coin is hardly worn, it should be nearly full weight. It is unlikely that a planchet from the previous, silver issue was used (1945) because of the 3 year time difference. Could be plancet intended for another coin. I assume it was struck by the Royla Mint London. Would be interesting to check what other coins with same diameter but with weight of 5 grammes, and silver, were minted there in 1948.