Last month HMRC released a useful video titled "Paid too Much or Too Little Tax?"
The video explains what to do it you feel you have over or under paid your tax.
If you have under/over paid your tax, HMRC will send out a letter notifying you of this fact.
This letter is sent between now and October 2015.
HMRC issues form P800 detailing the precise amount of tax you have under/over paid.
Please watch the video below: