These coins are still 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.
There were no British 1979 20 Pence coins minted.
There was no 1974 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 50 New Pence coin was issued in 1969.
The British 20 Pence coin was first released in 1982.
The first British 20 Pence coin was issued 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.
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.
2 British Pence in 1979 had the equivalent value of about 1 cent USD.
The 10 New Pence coin was not introduced until 1968.