oversea pension

I have a oversea pension of about 100000 pounds. but i have checked that there is a double taxation agreement with my previous country. and I do not need to pay tax on this pension. As I thought I do not need to pay tax, I didn't realized that I had to report in the previous tax year. what can i do now? and How can I state my situation in the self assessment?

Hi stanleylam,
You have not mentioned the country in question.  
A list of the tax treaties with the UK can be found at Tax treaties.  
As you are resident in the UK, it is most likey that your pension is taxable in the UK and not in the other country.  
You would declare the pension on SA106 Self Assessment: Foreign (SA106) when submitting your self assessment tax return.
Thank you.