Independence for Mill Hill

I've been told that Mill Hill is the largest postal district in the Borough of Barnet. Unlike many other parts of the Borough, although wealthy, the ward is marginal, having had a mixture of Lib Dem and Tory councillors over the last 20 years. Basically, unlike wards such as Totteridge, if the Tories put useless lazy pisstakers in Mill Hill they lose. What is it about the "Barnet" bit of Barnet. Villiers, Tambourides, Evangeli to name but a few. Is there any way a postal district can withdraw from a Borough and declare independence?