Hi,
On arrival in the UK, you will need to take the residency tests, to determine whether your are considered resident for tax purposes for the full tax year. If you are, then you will need to determine if split year treatment applies to you. If it does, you would claim split year treatment on SA109 and only declare your income and gains from the date you arrived in the UK, in a self assessment tax return (SA100). Income and gains for the period before you come to the UK, would not be taxable here.
Any foreign interest that is taxable in the UK, is declared as foreign interest on SA106, where you can declare any foriegn tax paid on the interest and claim a tax credit.
Personal allowance are allowed automatically, where you are considered resident in the UK for tax purposes for the full tax year and split year treatment does not apply. All your world wide income in the tax year would be declared in the tax return.
If the capital in the foreign savings account arises in tax years where you are not resident in the UK, then it would not be taxable, if remitted to the UK and does not need to be declared, only the interest it generates would need to be declared.
If split year treatment applies, then only the income and gains arising in the period you are resident in the UK would need to be declared.
Transferring capital from a foreign account to a UK account would not be taxable, unless all or part of the capital arise from income or gains the the tax year you arrived in the UK.
This is still the same even if you are not resident in the UK at the time of the transfer and become resident part of the way through the tax year.
When HMRC calculates how much tax you need to pay, it looks at your non-savings income first, followed by your savings income, and then your dividend income.
UK tax legislation requires income and gains to be taxed in a fixed sequence. This sequence is 'non' savings income, savings income, dividends, chargeable event gains and followed by capital gains.
Non savings income is the likes of 'employment' income, 'self employment' income, 'partnership' income and 'property' income. next comes 'savings income', which is tax and untaxed interest, which is always followed by dividends.
Thank you.