<P> Irish - register ships could fly the Red Ensign until September 1939, after the outbreak of World War II, when a decree under the state of emergency was made, to ensure neutral Irish ships were not mistaken for British ships . Some ships flying the tricolour were nevertheless sunk by Germans . When the tricolour was hoisted over the passenger ferries in Holyhead their British crews went on strike . Five days later their owners transferred the ferries to the British register and the Red Ensign was restored . On the other hand, the Belfast to Liverpool ferry, British owned and British crewed, used the tricolour as a flag of convenience; so did the whalers of Christian Salvesen Shipping, to take advantage of the Irish whale quota . </P> <P> The tricolour's marine status was formalised by the Merchant Shipping Act, 1947 . </P> <P> In 1921, Ireland was partitioned, with the unionist - dominated north - east becoming Northern Ireland, while later, in 1922, the remainder of Ireland left the United Kingdom of Great Britain and Ireland to form the Irish Free State . Northern Ireland continued to use the UK's Union Flag and created its Ulster Banner derivation of the flag of Ulster with a crown on top of a six pointed star . Furthermore, for many years the tricolour was effectively banned in Northern Ireland under the Flags and Emblems (Display) Act (Northern Ireland) 1954 which empowered the police to remove any flag that could cause a breach of the peace but specified, rather controversially, that a Union Flag could never have such an effect . In 1964, the enforcement of this law by the Royal Ulster Constabulary at the behest of Ian Paisley, involving the removal of a single tricolour from the offices of Sinn Féin in Belfast, led to two days of rioting . The tricolour was immediately replaced, highlighting the difficulty of enforcing the law . </P> <P> Despite its original symbolism, in Northern Ireland the tricolour, along with most other markers of either British or Irish identity, has come to be a symbol of division . The Ulster Unionist Party Government of Northern Ireland adopted the Ulster Banner (based on the flag of Ulster) in 1953 . Thus it is this flag and the Union Flag that are flown by unionists and loyalists, while the tricolour is flown by nationalists and republicans . In Northern Ireland, each community uses its own flags, murals and other symbols to declare its allegiance and mark its territory, often in a manner that is deliberately provocative . Kerb - stones in unionist and loyalist areas are often painted red, white and blue, while in nationalist and republican areas kerb - stones may be painted green, white and orange, although this is a much less frequent occurrence . Elements of both communities fly "their" flag from chimneys, tall buildings and lamp - posts on roads . </P>

Why should the irish flag always fly highest in ireland