These coins are still potentially in circulation so, unless they are part of a Proof or Uncirculated mint set or are individual Proof or Uncirculated coins and in absolute mint condition, they are worth 20 Pence.
A British 1997 cupro-nickel 20 Pence coin (heptagonal)(Elizabeth II)(Proof FDC), uncirculated and in absolute mint condition could fetch up to £3 GBP.
A reputable coin dealer will be able to give a more accurate valuation.
There was no 1974 British 25 Pence coin minted.
Yes. There were 89,518,750 British 20 Pence coins struck in 1997.
The British 20 Pence coin was first released in 1982.
Such a coin does not exist. The British 50 Pence coin was first issued in 1969.
There was no 1978 British 25 Pence coin minted.
1997 British 50 Pence coins do not have thistles or roses on either side. The 1997 coin has Britannia on the reverse.
The first British 20 Pence coin was issued in 1982.
The "face value" of a coin is whatever is inscribed on it, hence the term "face value". The face value of a 10 Pence coin is 10 Pence.
There were no British 1975 25 Pence coins issued.
The first British 50 New Pence coin was issued in 1969.
The term "New Pence" ceased to be used on British coins in 1981. The word "Pence" should have a numeral with it to indicate how many Pence. Pence being the plural of Penny. In 1997 there would have been 50 Pence, 20 Pence, 10 Pence, 5 Pence and 2 Pence coins and a 1 Penny coin.
The value of the copper in a 2 Pence coin would be significantly less then 10% of the face value of the coin at the time the coin was minted. Today, it might be a little more, about 0.2 Pence.