Thanks for commenting, Pedro. I think there are something like 5-6 million adult UK citizens who have permanently emigrated, so in theory they could make a big difference. The number now included under the 15+ year rule will be much smaller. And the proportion of those who have lived outside the UK for that long and will register to vote is probably fairly low.

Add to that the fact that their votes are spread across individual constituencies, and will probably be fairly evenly distributed in party terms, and it probably wouldn't make much of a difference.

The Australian rule is that expats can vote 'if they intend to return to Australia to live', which sounds reasonable - they have a long-term stake in their country's domestic affairs. But how on earth do you check up on that? You can hardly repeal their vote 5 years later if they're still settled in Singapore.

I don't think there's a simple answer to whether it's democratically right or wrong.

The basic principle is, I suppose, if a decision affects me, I should have a say in it. But 'affects' is a relative thing. I'm unaffected by UK health and education policy, but affected by foreign and pensions policy, for example. Maybe I should get half a vote.