Platfroms set up UK..but then leave


Hi there, Im an old sea dog, im UK based , but want to take the plunge.....(im gettng zilch on savings), I have a plan to invest quite a bit, in 4 or 5 blue chips, all div payers, and will be happy with 4 to 5 percent divs , plan, is, aside from reviews, leave for 5 years, and chuff off to live in Istanbul, (have lived there in the past, for shorts periods)....i wont add funds into the trading platform, as i probably cant, but question, what UK platform , will let me set up here in the UK, then leave to Turkey for a few years and not close it all down??...
If you're talking about simply buying shares, then surely any company that's likely to be still around a decade from now would do? What about the biggest and oldest broker / bank?
Thx, I asked the Halifax...they are old(ish) simple, low fees,etc, would have been ideal to leave,reinvest Divis, but, they said when you leave the UK they cannot hold an account anymore