If you are unhappy about this, speak to the manager at the Post Office you dealt with. Surely Post Office counters was acting as an agent for DVLA and they should have made sure they collected the correct amount. If they did not, then they should be aware of how this is normally corrected.

mattscott3011:

I cant see how they can enforce this

As I say, they can declare your current tax disc invalid. I had a situation when I bought a car (it was being sold "by order of the police" at an auction). It had a current tax disc but the cheque that had been used to buy this tax disc bounced, although I didn't find out about this until I'd had the car for a couple of months and I'd completed the procedure to register the car in my name. DVLC declared the tax disc invalid so I had to return it and buy a new one. They also said that I could be held liable for the car tax in the months between when I bought the car and when I bought a valid tax disc although they haven't followed this up with me.

You are liable to pay £445 tax if you want a 12 month disc. If you've paid £200, then you owe another £245. There's nothing wrong with asking whoever made the mistake to pay it for you but we both know what the answer will be.

Thanks for the reply.
The correct tax rate is £445. The letter does not saying anything about the tax becoming invalid.
The tax disc is valid for 12 months as stated on the disc itself.
I cant see how they can enforce this or say it runs out in say 186 days and the letter basically seemed like a letter saying "we know we have messed up please get us out of this jam".

Mistakes happen. You are liable to pay the car tax at the correct rate. An exception to this might be if the mistake happened a couple of years ago and then you could argue that it wasn't reasonable to be asking for payment at this stage.

Obviously you need to check the correct rate of car tax for your vehicle on a .gov.uk web site before you send any payment.

I expect that you've been notified (or, if you do nothing, you will be notified) that the current tax disc may become invalid. While it's unlikely that you could be stopped by the police at this stage, it is still an offence to drive without a valid tax disc.

I recently bought a car and got it taxed at the post office for 12 months. I paid the £245 they asked and went on my way.
2 weeks later i have received a letter from the DVA saying that the post office had undercharged me by £200 and that could I please send them a cheque for the amount.
They then says thanks for my cooperation and apologies for any inconvenience.
My question is whether or not I am liable to pay this as I paid what I thought was in full in good faith and the mistake was theirs not mine.
Also by the wording of the letter, which is not signed and is addressed to sir/madam, it makes me think that they cant enforce me paying this.
Some advice would be very welcome thanks in advanced.
P.s. this is in northern ireland so it is with the dvlni rather than the dvla.