Canada RSP

I am a Canadian citizen but left Canada in 1985 and have lived in the UK since then. I have an old compnay profit sharing scheme which has had no personal contributions since I left in 1985, and some RSP savings, which were merged together into an RSP some years ago. The value in 1985 was about $12,000 and has grown to $150,000, and I have just cashed it in at the end of this past tax year. There was a 25% Canadian witholding on the full maturity amount. Can I treat all or part of this as a capital gain, or is it all treated as taxable pension income for UK tax purposes?

Hi

This is a pension for tax purposes.
The guidance at DT4617, advises that 'Where a UK resident makes a lump sum withdrawal from a Registered Retirement Savings Plan (RRSP) or a 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. 

Thank you