What's needed to Tax my car?

[Niall]

Inorder to tax a car, you need a valid MOT and insurance. MOT can't be due to expire I.E, within 2 weeks of expiring i think it is to tax online. If you do it in the post office, you can do it even before the day the MOT runs out.
If you do it online on say for example the 29th of this month and on the 30th the last tax period runs out, you have 16 days (why 16 i don't know!) for the new disc to arrive and for you to put it in the windscreen. Tbh, they don't even check discs any more as its all online now hence why as of October this year, you will no longer get a disc.

Ah okay my tax runs out on 31/05/2014 and I'm taxing it on 01/06/2014 so I should have to wait 16 days if I do it online? And how do I prove I have insurance if I'm taxing it the same day as I insure it? Do I use the email that I'll be sent?

No what I'm saying is, if you tax it online you won't get a disc instantly. It will take a few days/week to turn up so they give you a 16 day grace period from the end of the previous tax before you have to display your new disc (idea being you have time for it to arrive). If you still don't display it after that, theres the chance of a 200 quid fine.
If you do it online, insurance is automatically checked on the MID. If you do it in the post office, you need to take a valid insurance certificate.