In what year was the current design of the Union Flag introduced?

The Union Jack, or more correctly Union Flag, is the national flag of the United Kingdom. The current Union flag's design has been in use since 1801.

The Union Jack is normally twice as long as it is tall, a ratio of 1:2. In the United Kingdom, land flags are normally a ratio of 3:5; the Union Jack can also be made in this shape, but is 1:2 for most purposes.

Flags that have the Union Jack in the canton should always be 1:2 to preserve the square fly area.

The three component crosses that make up the Union Flag are sized as follows:

The red St George's Cross width is  1⁄5 of the flag's height with a  1⁄15 flag height fimbriation.

The white diagonal St Andrew's Cross width is  6⁄30 of the flag's height, visible on either side of the St Patrick's Cross in diagonals of  1⁄10 and  1⁄30 of the flag's height, respectively.

The red diagonal St Patrick's Cross width is  1⁄15 of the flag's height. It is offset by  1⁄30 of the flag's height in anti-clockwise direction.

According to the official blazon of 1801, the white diagonal St Andrew's Cross is in fact counterchanged with the red diagonal of St Patrick's Cross. In this interpretation, the width of both saltires is  1⁄15 of the flag's height, with fimbriations of  1⁄30 of the flag's height on either side of the red saltire.