If you are resident overseas, the taxation of your pension income will largely depend on what type of pension is being received and the tax rules in your country of residence.
When residing in France, if a pension arises from government service, it will remain taxable in the UK, under the UK/France Double Tax Treaty. UK Government Service Pensions are not taxed directly in France, but the income is taken into account for the purposes of determining the rate of tax payable on other French source income (taux effectif).
Otherwise, the pension will be taxable only in France, at the usual scale rates (top rate is currently 40%). There are minor allowances available against Personal Pension and Occupational Pension income.
In certain circumstances and with careful planning, a significant percentage of your annual pension income could be tax free in France.
Social charges may also be payable, depending on the type of pension income, but only in certain circumstances.
Currently, pension lump sums are not taxable in France.