Yes 603L is the emergency tax code for the current financial year. The emergency tax code is set each year and is a number followed by the letter L. The number is the basic Personal Allowance (£6,035 for the tax 2008-09) divided by 10. It just so happens that 603L is also the tax code for most normal workers in the UK who are single. Unless you are a single parent or similar, this tax code is probably the correct tax code. If you are in doubt contact your local HMRC office.