356grams. The 1p weighs 3.56grams and the 2p weighs 7.12grams. Whichever combination you use, for £1, it should always weigh 356grams.
Nobody invented it. The traditional English coins were originally based on those current in the Dark Ages in western Europe.
The golden coins of the Roman Republic named aureus. The silver coins of the Roman Republic named denarius. The bronze coins of the Roman Republic named sestertius and dupondius. The copper coins of the Roman Republic named as.
Six obols made a drachma. Copper and silver coins.
Pounds, Shillings and Pennies, mostly sterling silver or gold coins, (no paper money).
England is part of the United Kingdom. The currency of the United Kingdom is the Pound Sterling (symbol: £, abbreviation: GBP). The Pound Sterling has coins in denominations of 1p, 2p, 5p, 10p, 20p, 50p, £1 and £2. Banknotes are issued by the Bank of England in denominations of £5, £10, £20 and £50. Wales, Scotland, and Northern Ireland are part of the United Kingdom as well, and also use the GBP.
If you refer to the scrap value of the copper, there is no copper in British "copper" coins these days.
Pure copper has not been used to make British coins for about 150 years. From 1860, British "copper" coins were made from bronze which consisted mostly of copper varying from 95 to 97% copper. From 1992, British "copper" coins were made from copper plated steel. Ironically, copper is used to make modern "silver" coins (cupro-nickel) consisting usually of 75% copper and 25% nickel.
In 1892, British coins were made as follows - Pennies, Halfpennies and Farthings were made from bronze. Crowns, Halfcrowns, Florins, Shillings, Sixpences, Threepences and Maundy coins were made from 0.925 sterling silver. Sovereigns and Half-Sovereigns were made from 22 carat gold.
British coins of copper appearance, the 1 and 2 Pence coins, are made from copper plated steel. British coins of silver appearance, the cupro-nickel 5, 10 and 50 Pence coins, are made from 75% copper and 25% nickel. British 20 Pence coins, are made from 84% copper and 16% nickel.
Assuming you refer to the 1981 British 25 Pence coin (Crown), it is made from a copper-nickel alloy. If you have a sterling silver Proof coin, it will state somewhere on the packaging that the coin is made from sterling silver.
The British silver coinage was degraded from 1919/1920 from sterling silver to 50% silver. All British silver coins from 1919/1920 to 1946 inclusive had a 50% silver content. From 1947 onwards, all circulating British "silver" coins were made from a copper-nickel alloy.
The were no British or Australian coins made from pure copper in 1915. Pennies, Halfpennies and Farthings were made from bronze which was about 97% copper.
In 1900, British "gold" coins were made from 22 carat gold (91.67% gold content). These included the whole range of Sovereign coinage. British "silver" coins were made from sterling silver (92.5% silver content). These included the Crown, Halfcrown, Florin, Shilling, Sixpence and Threepence. British "bronze" coins were made from 95% copper, 4% tin and 1% zinc. These included the Penny, Halfpenny and Farthing.
Circulating US coins were struck in "coin silver" which has more copper in it than sterling silver. The extra copper was needed to make the coins hard enough to not wear out quickly. Please see the Related Question.
The copper content of 20th century British predecimal Pennies, Halfpennies and Farthings varied from 95.5 to 97%. When the use of silver in coins was discontinued after 1946, all British "silver" coins were made from a copper-nickel alloy consisting most commonly of 75% and 25% nickel.
If you intend to "scrape" the copper off for personal gain, most countries have laws concerning the mutilation and disfigurement of their coins.
US circulation coins prior to 1965 were made of coin silver, not sterling silver. Coin silver has more copper in it for hardness, so that the coins wouldn't wear out as fast.