The National Symbol of England / Государственная эмблема (Национальный символ) Англии
The red rose is the symbol of England. It comes from the history of the country.
This symbol goes back to the War of the Roses, which was the war within the country. In the 15th century two Houses were struggling for the English throne — the Lancastrians and the Yorkists.
Red rose was the emblem of the Lancastrians and the white rose was that of the Yorkists. Their rival ended when King Henry VII, the Lancastrian, married Princess Elizabeth, the daughter of the Yorkist. Since that time the red rose has become the national emblem of England.
An oak is also depicted as the national symbol of the country.
The National Symbol of Scotland / Государственная эмблема (Национальный символ) Шотландии
For many centuries the purple thistle has been Scotland's national emblem.
There is a legend that explains why it became the Scottish emblem. According to that legend, ancient Scandinavians (the Norsemen) wanted to plunder the land of Scotland and settle there. So, they landed on the east coast of Scotland.
The Scots gathered their army to defend the land. They assembled behind the river Tay and made a camp to have rest after a long march. The Scots were sleeping and did not expect the enemies.
When the Norsemen decided to attack the Scots, they took their shoes off not to make noise. But one of the Norsemen stepped on a thistle. That sudden and sharp pain made him scream. So the Scots heard this "alarm" and put the Norsemen to fight.
That is how the thistle became the emblem of Scotland.
The National Symbol of Wales / Государственная эмблема (Национальный символ) Уэльса
Wales has got two national symbols. These are the daffodil and the leek.
They are both connected to the Patron Saint of Wales.
According to the legend, during a battle against the Saxons, St. David advised his soldiers to wear leeks in their hats so that they could easily be distinguished from their enemies.
Another link between the leek and St. David is the belief that he had to live on bread and wild leek for several years.
However, today each year on St. David's Day the leek is worn in the cap badges of every soldier in every Welsh regiment.
But outside the army, many other Welsh people have substituted the leek by the daffodil, perhaps because it looks more attractive and certainly smells a lot better.
The daffodil is also associated with St. David's Day, due to the fact that it breaks into blossom on that day. Interesting to note that one of the many Welsh names for a daffodil is "Cenhinen Bedr" which means "Peter's leek".
The National Emblem of Northern Ireland / Государственная эмблема (Национальный символ) Северной Ирландии
The shamrock is the symbol of Northern Ireland. It is also connected to St. Patric, Patron Saint of Ireland.
Sa 
int Patrick is most famous for bringing Christianity to Ireland. The legend tells how he used the shamrock, a kind of a white clover with three leaves to explain the Holy Trinity. Apparently, he used it to show how the Father, the Son, and the Holy Spirit could all exist as separate elements of the same entity.
The red hand is also a symbol of Nothern Ireland. The Red Hand is in its flag. According to the myth, there was time when the heir to the throne of Ireland was undecided. And they decided to hold a boat-race and the winner (the first who would reach the shore of Ulster) would be the king. One competitor so much desired the country that when he saw that he was loosing the race, he cut his hand, threw it to the shore and won. The hand is most likely red because it was covered with blood.