When you hand in your notice it takes effect from midnight that you hand it in. If it says 1 months notice and you hand it in on the 14th of March, you would have to work up to and including the 14th of april. You would have to work it, unless you employer said other wise. If your employer asked you to leave early and not work your notice he would still ahve to pay you for the remaining notice period. Also you can serve out your notice while on the sick or tkae holiday during your notice period. If you decided not to work your notice period, and your employer wishes you to work it, he could take you to civil court for breech of contract and claim for how he has been financhally inconvienced (eg had to get a temp in for that time, could claim the cost of the temp)
Based ok UK Legislation