Bet the police will love that! If people already pull the stunt of cancelling their pay-monthly insurance and driving without cover, you can just imagine the excuses that'll crop up with the tax... "well officer, I set up the direct debit, it's not my fault if the government haven't been taking the payments" when actually they cancelled the direct debit months ago.
As for the SES tax disc holders... perhaps they'd make a good mobile phone cradle for in the car or somewhere to store petrol receipts or something?