The UK Government recently changed the rules on postal voting for British Citizens who are resident abroad and reduced the length of time that they are eligible to vote after moving abroad to 15 years.
This is despite the fact that HMG reserve the right to tax "Government Pensions" in the UK. Thus both my wife and I continue to be taxed in UK (she was in Teaching) but will lose the right to vote in the election of the Parliament that sets the level of taxation that we have to endure.
Of course if one resides in a country which does not have a dual taxation treaty with the UK you get the double whammy.