Since you have been living and working in the UK, have you received non-UK income or gains which have not been brought into the UK of £2,000 or more per tax year?
Have you been completing tax returns since you came to the UK?
Leave this with me while I draft my answer. It will take a while som please bear with me.
Take a look at Section 9 of RDR1 here.
Where in any one tax year, you have non-UK income which has not been brought into or remitted to the UK, then you either have to pay UK tax on it or make a claim via a tax return for the remittance basis to apply so that you don't pay UK tax on it.
Once you have been resident in the UK for seven of the previous nine tax years, if you wish to use the remittance basis of assessment for any tax year, you will have to pay the remittance basis charge of £30,000. Clearly, you would not do that unless you had very high non-UK income and gains. See here.
As you appear to have done nothing so far, I would recommend that you find an accountant or tax adviser who can advise you on what the potential tax liabilities are for the tax years you have been in the UK assuming you cannot backdate a claim to the remittance basis and to ask HMRC if you can claim the remittance basis retrospectively if that would be to your advantage. An accountant or atx adviser can deal with HMRC for you. Any foreign tax you paid on income and gains charged to tax in the UK can be offset against that UK tax liability assunibg your home country has a tax treaty with the UK.
I hope this helps but let me know if you have any further questions.
A phone call will involve an extra fee so you might prefer to continue here. Let me know either way.
Is the balance now the same as when you first came to the UK?
If you were coming to the UK to live now, I would advise you to isolate the bank balances you have now and if you earn any non-UK income from now onwards that you don't bring into the UK to bank it in a separate account. The same applies to capital gains. Basically, the cash you had made before you came to the UK can be brought in tax free.
I'm just following up to find out if my answer helped or if you have any further questions