From 1st October 2014 you no longer need to display a tax disc on the windscreen of your car, if you have a Tax Disc that expires in October, November or December or beyond (for those who buy 12months worth) then you can either remove it after 1st October or Continue to Display it until it expires, After this date your vehicle will only be taxed once you've paid for it online, the DVLA will keep a record of your vehicle being taxed on their systems.
https://www.gov.uk/government/news/vehicle-tax-changes