If you're thinking of spending "several months out of a year in Turkey" then I assume that you could be in the UK or other European country for the remainder and would still need to access this money. You may find it easier to have your pension(s) paid into a your UK account and then draw it down to a Turkish account as required because you might struggle with accessing a Turkish account when out of Turkey.
As far as I'm aware the UK / TURKEY DOUBLE TAXATION AGREEMENT 1988 is still in force. That means that you WILL pay tax on your pension, but only in one country. Therefore, if you pay tax at source on your pension in the UK and have proof of that, a recent P60 was sufficient when we opened our Turkish bank accounts, you won't be paying tax on it in Turkey.