The root of this may be the tax code used by your three pension providers.
You should remember that although your State pension is paid free of tax it does, in fact, form part of your taxable income. (Your tax code should have been reduced to account for this). This means that if the total of your State pension and private pensions exceed the tax-free allowance (which was £8,105 for 2012-13) then tax will be payable on the excess Also bear in mind that, unless you have told the tax office to inform them individually as to how you want your tax deductions handled, each of your three pension providers might be allowing too much tax free.
I can understand if you don’t want to share the information publicly, but if you do, give me your income figures and I will calculate the tax due.