Some assumptions to start with:
You've earned £30,000 roughly for each of the past 3 years, from an employer. You are not self-employed. You have a current bank account and possibly a small savings account. You do not have dividends, etc., or any other source of income including UK benefits. If there is anything different, or in addition to the above, the following may need adjustment. Are you single, or married?
Don't be too nervous. You're in company with thousands of others. Sorting this out may take some time and effort, but normally there are no 'bad things' that will happen to you if you act now.
First, let's dispel one major misunderstanding. Because you earn less than the form 2555 threshold of roughly $100,000 per year does not mean you don't owe tax on that income. The only way to claim the exclusion and avoid the tax due is to file a tax return. Without filing, you owe the money.
You are a prime candidate for the new
'Streamlined Filing Compliance Procedures'. You would need to file returns for each of the past 3 years. See the following links:
http://www.irs.gov/Individuals/International-Taxpayers/Streamlined-Filing-Compliance-Procedureshttp://www.irs.gov/Individuals/International-Taxpayers/New-Filing-Compliance-Procedures-for-Non-Resident-U.S.-TaxpayersEDIT: this contains some examples:http://www.irs.gov/Individuals/International-Taxpayers/U-S-Taxpayers-Residing-Outside-the-United-StatesYou will need to follow the instructions for the programme. The forms you will likely need to begin are form 1040, Schedule B, form 2555, and form 8965 (for 2014 only). Depending on your circumstances, there may be others.
You may also need to file 6 past years of FBAR's (FinCEN 114), if you meet the requirements and threshold for filing each of those years. You may need to file form 8938 if your bank account(s) had over $200,000 in aggregate at 31 December for any of those years.
You need your own accurate records for income in case of questions, but nothing needs to be filed with the tax return. UK banks and employers do not issue anything similar to a 1099 on a calendar year basis, so it will be your word regards the accuracy of your return.
Remember, the UK tax year (and P60's) are based on the UK tax year, which is different from the US tax year.
DO NOT consider the OVDP programme unless you have wilfully practised tax evasion.