One problem that the UK government may raise is to where overseas citizens should vote.
Fortunately, some 93 countries allow their citizens overseas to vote - see
The French and the Italians approaches might be the most interesting.
In 2001 France redistributed the number of seats in its Assembly and created 11 new electorates based on geographical location.
There were 577 seats before the distribution and 577 afterwards. Of the regions, the 11th covers 48 countries to include Australia.
Since 1982, citizens overseas were also able to vote indirectly for Senators through the Assembly of French Citizens Abroad
Italy has always allowed citizens living outside the country to vote but one had to return to Italy to do so. In 2001, they were allowed to use postal votes provided that they were registered with their local consulate. They had 12 seats in the Chamber of Deputies and 6 seats in the Senate. This was apparently reduced to 8 and 4 in 2019.
It would be nice to see the UK do something similar.