Hello, I am Keith, one of the experts on Just Answer, and pleased to be able to help you with your question.
It is routine world wide for pensions to be taxed in country of origin. You then use the numerous Double Taxation Treaties, which preclude the same income stream from being taxed in both jurisdictions, by using the UK tax deducted as a tax credit against any liability in the other country. You will, of course, be entitled to your Personal Allowance of 11K which will reduce your UK taxation. You should get your pension provider to operate PAYE on your pension once it is in issue. Many insurance companies do not like operating PAYE. I personally dragged two household names screaming and kicking into compliance on tax deductions.
One point, as an ex pat, when you left the UK did you complete a Form P85 and send it to HMRC? If you did not you should do so immediately, fortunately there is no time limit as to its submission, it is available on the web and can be filed on line.. On receipt HMRC will classify you as non resident and you will find dealing with that Department much easier. Once so classified you can spend up to 91 days in the UK without breaching your non resident status.
I do hope that you have found my reply of assistance.