A burka ban is excessive relative to its object
The burka is worn by less than 1% of Muslim women. A blanket ban is not a proportional response in relation to the object.
A burka ban would infringe Muslim women's rights to religious freedom and civil liberties.
In some places, including the Spanish town of Lleida, attempts to ban the burka have been overturned in national courts over concerns that it restricts religious liberties.
For those who interpret Islam's teachings as requiring them to wear a burka for their faith, they should be free to do so in the same way as anyone else who chooses religious clothing. While the UK does not have a written constitution which heralds individual liberty in the same way the USA does - primary legislation including the Human Rights Act protects freedom of speech and religion. Under this legislation, the wearing of religious attire, including crosses, kippahs and Islamic veils, is protected as a civil right.
The Burka is Not a Religious Freedom The burka is not an essential part of the Islamic faith. It is a personal choice. Therefore, banning the burka is not a violation of someone's religious freedoms. They are still free to practice the Islamic faith and are able to do so, free from restriction, harassment or hindrance. 
[P1] Freedom of expression and religion is a civil right. [P2] A burka ban would infringe that right. [P3] Therefore, burkas should not be banned.
[Rejecting P2] A burka ban would not infringe that right because wearing a burka is not an essential facet of Islam.