Stumbled across this whilst trying to change the address which HMRC have registered for me.
I didn't know it existed so thought it might be helpful to others too...
You need to first setup a Governemt Gateway account then you'll be able to login to view things like:
- Your Tax Contributions
- Your Tax Code
- Your NI Contributions
- Your Pension Forecast
- Tax Credits etc...
- Update your personal details (address etc...)
Probably not useful for everyone but I found it pretty handy.