Hi John Smith,
The guidance at DT4617, advises that 'Where a UK resident makes a lump sum withdrawal from an Registered Retirement Savings Plan (RRSP) or an Registered Retirement Income Funds (RRIF), Canada imposes a 25 per cent withholding tax'. (
DT4617 - Double Taxation Relief Manual: Guidance by country: Canada: Withdrawals from Canadian RRSPs/RRIFs).
No tax credit relief is allowable, which means that the full lumpsum is taxable in both Canada and the UK.
You can, however, claim a foreign tax credit relief of up to 100% of the foreign tax deducted, against your Uk tax liability.
It is only the retirement savings plans or registered retirement income funds that would be covered by DT4617.
If you are a UK resident, you are taxable on the TFSa and FHSA in the UK, under world-wide income.
Thank you.