Various British coins dating back hundreds of years have had a shield of one type or another on the reverse. The only current British coin to have a full shield is the new design One Pound coin first issued in 2008.
The gate, or "Portcullis" on the 1971 to 2008 British Penny is taken from the Badge of Henry VII, and is now the Badge of the Palace of Westminster.
The structure on the reverse of the Penny is a "crowned" portcullis (or gate).
A portcullis is a heavy metal grate used as a gate. The guards raised the portcullis of the castle.
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You can buy any non-circulating British coin from the Royal Mint in the year of issue. For older coins, you would need to see a coin dealer.
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There are no British Pennies with pigs on them. All British One (New) Penny coins have a Crowned Portcullis with chains on the reverse.