@gaz1
I claim a UK private pension and have been doing so for over four years now.
I've also made lump sum draw downs.
Firstly, there is an agreement between the UK and Bulgaria of single taxation only, so you can only be taxed once.
Secondly, you will find that when your pension administrator pays your pension every month, income tax is deducted automatically (as PAYE). This is how my pension is paid.
You can, however, notify your Pension administrator and HM Revenue and Customs, that you wish to be registered under the Bulgarian tax authority. However, this may not be as straightforward as it might appear and that is why I have not gone down that route.
Firstly, you would have to rely on your pension administrator remembering not to deduct tax every month. If your administrator deducted tax by accident, you'd then have the, very laborious, task of having to claim it back from HMRC. Further, this could easily lead to your tax code being altered against your favour. I have already had an issue with my tax code and I spent nearly an hour and a half on the phone (most of that time, spent waiting to be connected) getting it sorted out.
Further, you may also find that your pension administrator is obliged to deduct tax (PAYE) and you may be told that it is your responsibility to claim it back from the HMRC,.
Whilst the Bulgarian "state" pension is not taxable, I'm not at all sure of how the Bulgarian authorities view "private" pensions. If, however, private pensions are taxable in Bulgaria (I'd be interested to know if anyone has confirmed this) there is the other issue, that Bulgaria does not have a tax allowance, so you would not get the £12,570 tax allowance that you get in the UK. Of course, the tax rate in Bulgaria is lower at only 10%, so it's swings and roundabouts.
I worked out the tax difference between the two countries on my yearly pension and it's around £450 more tax in the UK, taking the personal allowance into account.
On the subject of lump sum payments, you are entitled to a tax free lump sum. You can "crystallise" up to 25% of your pension pot and take it tax free. So, for example, if your pension pot is £250,000, you could crystallise £62,500 and drawdown on it without paying tax. You not have to take the full 25% in one go, you can draw it gradually, as and when you need to. This has the advantage, that your pension pot retains more in it to invest.
Lump sum crystallisation is also another reason to keep to UK taxation.
Hope this helps
Ian