As long as you are an EU citizen or have the unrestricted right to live and work in the EU, you do not need any special authorisation.
Taxes depend entirely on your circumstances, i.e. which tax bracket you fall in. Upon starting employment you will have to apply for a NI (National Insurance) number and your taxes are paid in the UK, as this is where you are employed unless specified otherwise, and taxes will be decducted automatically from your salary. However, at the end of the fiscal year, you can do a self assessment and may be eligible for tax returns depending how clever you are about these things.
Hope this helps.