Do you have a British coin, which was used in circulation, and do not know if its rare or not?  Below is a guide on the very rare and expensive (Price over 100 pounds for FINE condition) British 19th and 20th century Silver, Copper and Bronze coins, which were issued for circulation.

The Crown:  1847 Victoria Crown, Gothic Type
                    1932 George V Crown
                    1934 George V Crown
                    1936 George V Crown

The Half Crown:  1823 George IV, Reverse side with a garnished (fancy) shield, thistle and shamrock on either side, date under.

                   1824 George IV, Reverse side with shield with creat, date under Kings's Head
                   1841 Victoria.
                   1903 Edward VII  
                   1905 Edward VII
                   1952 George VI

The Florin: 1854, 1862, 1863, 1867 (42 arcs) 1877 (no die number) 1879 (42 arcs), Queen Victoria Gothic Type

The Shilling:  1850, 1851, 1854, 1857 (inverted G in DG), 1863,
                       1866 (BBITANNIAR), Victoria.  Edward VII - 1905

The Six Pence:  1862, 1863, 1878DR - Victoria

The Four Pence:  1837 - Victoria

The Three Pence:  1868 (RRitanniar error) - Victoria

The Penny:  1827 - George IV, 1843 (no colon after REG),
                   1860 (Copper), 1862 (small date like Half Penny),
                   1863 (die number by date), 1869, 1882 - Victoria,
                   1933 - George V

The Half Penny:  1862 (die letter to left of lighthouse)

The Farthing:  1860 (Copper), 1874Hg,