The HMRC OOTLAR (Overview of Tax Legislation and Rates) 

Useful for all up to date rates.  

HMRC pension page for Employers listing their responsibilities. 

The HMRC Business income manual will help to break down some of the specific tax rules for your type of business. 

HMRC's guide to VAT registration

If you're taking on your first empoyees, here is the guide to get started.

Filing obligations for your Limited company accounts on Companies House. What you need to file and when.