If this money is paid to you as a lump sum, and any tax due on the interest was covered in Singapore, then HMRC would not need to know about the transfer. They would, of course, need to know about any interest accrued on it once it is in your Lloyds account, unless tax is deducted at source before interest is added.
I understand the Central Provident Fund payment is not taxable in Singapore. As you rightly say, it is not an income payment but rather a capital sum, so again HMRC would not count it as income.
It doesn’t need to be ringfenced. As far as I can ascertain from the CPF website, it has to be paid out as a lump sum – almost like a maturing savings plan. If it had to be ringfenced when taking it out of the country, it would have specified that it has to go into some sort of pension arrangement – and that is not the case.
Forgive me if I’m telling you something you already know, but the fact that you don’t have a tax return to complete does not absolve the individual of responsibility for informing HMRC about sources of income that may not otherwise have been taxed. If in doubt, it is best to inform your local tax office.