A British 1950 Mid-Century coin set (George VI)Proof FDC - 9 coins - Halfcrown to Farthing), in absolute mint condition and original packaging, could fetch up to £135 GBP.
The values quoted are the best possible for the best specimens in their grades, but may be significantly lower due to varying demand for the coin and the prevailing economic climate. A reputable coin dealer will be able to give a more accurate valuation based on inspection of the coin.
Halfpenny - British decimal coin - was created in 1971.
Penny - British decimal coin - was created in 1971.
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.
Such a coin does not exist. The British One Pound coin was first issued in 1983.
The first British 10 Pence coin was issued in 1968 as part of the conversion to decimal currency.
In British Decimal currency, the One Pound coin was first issued for general circulation in 1983. The British Two Pound coin was first issued in 1985 as a collectible gold coin. It was first issued as a nickel-brass Commemorative in 1986, and as general circulation coin in 1997.
Until the introduction of decimal currency, British Threepences have been minted for hundreds of years. The value of any coin would depend on the year, the design, the metal it is made from and the condition of the coin.
You need to provide the year. Without knowing the year it is impossible to value your coin. Crowns (5 shilling) pieces were minted in several different years and have vastly different values depending on what year they were minted in.
A 10 New Pence coin was a British coin released as a part of the first phase of the conversion to decimal currency in 1968. It replaced the Florin or Two Shilling coin.
The first British 20 Pence coin was issued in 1982.
Please check your coin again and post a new, separate question. The term "new pence" was first used in 1968 when Britain began the changeover to decimal coinage.