I wish I had done as lucy did and relinquished my US citizenship when I became a UK citizen, but unfortunately I did not. Too late now.
Whatever you do, don't let this get you down!!!
It's a rum game when a retired person, at this stage in their life, wishes to open a new account to try to better their now limited funds only to discover this pile of muck awaiting.
There are usually 4 very basic options for someone in this situation. There could then be alternatives to each of the options.
1) The person could attempt to relinquish due to acquiring UK citizenship with the purpose of relinquishing US citizenship (as has been noted), even if it was in the past, as long as they have evidence that they wished to do so. Or, they may have had UK Govt. employment in the past, and have the evidence that this required an oath to the UK (the oath could be a relinquishing act).
In both cases, one would need strong evidence, and even then, the attempt may be not be accepted by the US Dept. of State as a relinquishing act. If such an act were accepted, and the act was after 2004 (don't you have all the luck), tax returns (varies to 2008) are likely required, unless they wish to also combine with option#3 on the tax front. There would be no fee involved.
2) They become compliant via the Streamlined Program if not already compliant, file 5 years of past 1040 returns, file 6 years of past FBARs (FinCEN 114), renounce US citizenship and pay the fee, and file a final dual return including Form 8854 (the Exit tax) the following year. This is a clean separation from the US and any obligations, as well as allowing full use of UK financial opportunities.
3) They renounce US citizenship and pay the fee. Since this is a stand alone act, they ignore their obligations to file with the IRS. They now become a covered expatriate. They will always be liable if found (don't go to the US!) and there would be penalties and possibly an abnormal amount of tax due if discovered. It would also affect any inheritance they wished to leave for someone resident in the US. It's risky.
4) They have been flying under the US radar for many years without filing a tax return. Nothing has changed as long as they never acknowledge they are a US citizen (say, to a bank or building society if asked). They simply deny they were ever a US citizen, although a US place of birth may easily give the game away, and they don't have a CLN. This is
obviously a very risky proposition although some may be willing to risk it. It creates problems in both the US and the UK (lying to a UK bank).
There are really no additional options other than becoming compliant (Streamlined Program) and keeping US citizenship (and filing returns and FBARs) for the rest of your life.
In your case, other than the problem opening an account, you have been flying below the radar for 50 years. There is no need to now take drastic immediate action. Give this whole mess some thought for a while before acting.
And you, be well!!!