If you start to get taxable company benefits, for example if you change jobs or get promoted, you should tell your tax office right away so that you don't get a large tax bill at the end of the year. The company doesn't have to tell your tax office about any company benefits you get until the end of the tax year, unless it's a company car.
You should also tell your tax office if you stop getting taxable company benefits. They can then change your tax code and make sure you don't pay too much tax. Either way, if they change your tax code you should receive a new PAYE coding notice.
If you are a higher rate tax payer, you are eligible to claim additional tax relief on your own personal contributions to a group personal pension plan like PensionSaver.
If you complete a self-assessment tax return you can include your contribution level in the return. However if you don't complete a tax return or wish to receive the additional tax relief immediately, you can arrange for your tax code to be amended.