You didn't state what the error is, but the most famous mistake(*) on 20p coins is a recently-discovered variety that's missing the date. See the related question for more details.
(*) Note that paper money is printed, but coins are minted or struck.
Misprinted coins, including those with errors like off-center strikes or missing elements, can sometimes be valuable to collectors. The value of a misprinted coin depends on the rarity of the error and the demand among collectors. It's best to consult with a specialist or appraiser to determine the specific value of a misprinted 20p coin.
It is worth 20p.
Misprinted coins can sometimes be worth more to collectors, but it ultimately depends on the specific nature of the misprint and the demand for such items. It's best to consult with a coin expert or collector to determine the potential value of your misprinted 2 dollar coin.
A "misprinted" coin is called an "error coin". These occur when there is a malfunction of stamping machines or a case of human error. The result is a coin which is not perfectly struck or has a design flaw. In order to give an accurate estimate of value, the exact nature of the error must be known. Please examine your coin again and then submit a new question giving a description of the error.
It depends on the country and the currency in use. For example, the US has a 25c coin but not a 20c coin. In the UK there is a 20p coin but not a 25p coin.
The 2008 mule 20p is more valuable than other 20p coins because it is uncommon and desirable to collectors. If the United Kingdom switched to the Euro this would not change the value of the coin as a collectors item, in fact it would probably make the coin slightly more desirable.
Britain introduced a 20p coin on 9 June 1982.
The coin is likely damaged, but take it to a coin dealer or collector, error coins need to be seen for an assessment.
Error coins need to be seen, take it to a coin dealer. Most errors are very common and add no value.
All error coins need to be seen. Take it to a coin dealer in your area.
It's a Heptagon
1982
In British coinage 20p coins are quite common and will normally only be worth their face value. The only notable exception is the 'dateless' 2008 mule errors which are worth significantly more than their face value. (around £30-£90)