That is a far too extensive a question to answer here, and also depends on what your definition of "value" is. The coins of greatest value are all locked up in museums and the collections of the very wealthy.
A rule of thumb is that with a few exceptions, all British decimal coins other than Proof or Mint Uncirculated coins, have little or no value above face value.
For predecimal British Coins, you will need to consult a coin catalogue and check your coins against the descriptions and conditions of the coins and look out for any rarities, errors or peculiarities. Proof and Mint Uncirculated coins will always have a relatively higher value.
The following coins are the most sought-after after the year 1900
CROWNS
1928, 1929, 1930, 1931, 1932, 1933, 1934 and 1936
HALFCROWNS
1903, 1905, 1925, 1930
FLORINS
1905, 1925 and 1932
SHILLINGS
1905, 1908, 1909
SIXPENCES
1904, 1952
BRASS THREEPENCES
1937 EDWARD VIII
1946 AND 1949
PENNIES
1902 WITH A LOW HORIZON BEHIND BRITANNIA
1918H (SMALL H TO THE LEFT OF THE DATE)
1918KN (SMALL KN TO THE LEFT OF THE DATE)
1919H
1919KN
1926 ME (MODIFIED EFFIGY - BM WITH NO STOPS ON THE BOTTOM OF BUST)
1933 - ONLY 7 KNOWN
1952 - ONLY 1-2 KNOWN
1954 - ONLY 1 KNOWN
HALFPENNIES - 1902 WITH A LOW HORIZON BEHIND BRITANNIA
FARTHINGS - NONE
There really are no post-decimalization coins intended for circulation that are valuable. There are two major error coins since decimalization that are worth more than face value. The 1983 Two Pence coin that says "New Pence" on the reverse of the coin is worth several hundred pounds. The undated 20 pence piece is worth quite a bit of money too. This coin has no date on it, but features the new reverse (the one with a portion of the shield, not the Tudor rose).
Of course, specially made collectible coins such as gold sovereigns, silver proof sets, gold one pound coins, etc. are all worth well over their face value, but as for circulating post-decimalization coins there aren't any worth over face with the exception of the 1983 New Two Pence coin and the undated 20p.
The most valuable British coin from 1902 would easily be the gold Five Pound (or quintuple Sovereign) coin. An uncirculated coin in absolute mint condition could fetch up to £1,600 GBP.
I
It does not stand for anything, it is the last syllable of BRITANNIA. The word is often split on some of the older British coins.
The first coins made in Britain were gold coins struck by the Celts in or around 70 BC. Prior to that, there were imported coins circulating, dating back to about 150 BC.
All British coins from 1911 to 1936 inclusive, feature King George V on the obverse. All British Pennies for hundreds of years until the last predecimal Pennies were minted in 1967, feature the figure of Britannia on the reverse.
Please check your coin. The last British Guinea or any of the fractional Guinea coins was issued in 1813.
British Guineas were no longer minted after 1813. They were replaced by the Sovereign.
around 200 years.
The Royal Mint produced no Half-Farthing coins after 1856.
The last British One Guinea coin struck for circulation was dated 1813.
The New Zealand Florin (Two Shillings) was first issued in 1933 and last issued in 1965. The most valuable New Zealand Florin would be 1936 coin. A distant second would be the 1940 and 1946 coins. The 1946 coin with the value shows the kiwi with a flattened back. It should be noted that the valuable coins only have the high value if the coins are in "mint uncirculated" condition.
The Bank of England advises that the life span of a banknote ranges from 1 to 5 years. The lower denomination notes that are handled more often have a relatively short life span, the Fifty Pound note may last for 5 or more years.
In 1917, British "gold" coins were made from 22 carat gold (91.67% gold content). British "silver" coins were made from sterling silver (92.5% silver content). British "bronze" coins were made from 95% copper, 4% tin and 1% zinc.
Prior to 1910, Australia used the British currency. British coins continued to circulate with Australian coins for many years. The Australian coinage was first introduced in 1910 and included the Threepence, Sixpence, Shilling and Florin. All coins were based on the equivalent British coins and were made from sterling silver. The following year in 1911, the One Penny and Halfpenny coins were introduced, again all based on the equivalent British coins and were made from bronze. Paper money was introduced in 1913. In the early 1960's, it was decided that Australia should have a decimal currency rather than the cumbersome British Imperial style of currency. It was eventually decided that Australia would adopt the Dollar of 100 cents as its currency. The last of the predecimal coins were minted in 1964. On the 14th of February, 1966 the new Australian decimal currency was issued to a well prepared Australian public.