These coins have only just been released into 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 5 Pence.
The British Five Pound (Crown) coin is not a general circulation coin, but has a face value of Five Pounds.
They are usually issued by the Royal Mint as a Proof coin in cupro-nickel, or silver or gold and will be valued accordingly.
There was no 1974 British 25 Pence coin minted.
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.
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 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.
Such a coin does not exist. The British 20 Pence coin was first issued in 1985. They are heptagonal, not round.
It is in common circulation and worth 2 British Pence, or about 3 cents US/Canadian. It is a common coin and worth no more than face value.
In 1944, the British used Pounds, Shillings and Pence. The British have never used cents. There has never been a British 10 cent coin and the British 10 Pence coin was first issued in 1968.