And that could play a significant role in how the European Parliament is made up for its next five-year term.
Currently, there are 751 seats in the parliament; but when Brexit happens that will go down to 705.
The minimum number of seats-per-country at the moment is six for the smallest nations: Malta, Luxembourg and Cyprus.
Germany has the most seats because it’s got the largest population in the EU.
Once the UK leaves, its 73 seats will be redistributed. The plan is to leave some for any new countries which join the EU.
Other seats are set to be shared around current members. Spain and France will benefit the most. The Netherlands and Ireland will do well proportionally for their size.
And there are a number of other EU countries who’ll all be given one extra seat each.
If Brexit does happen on October 31 as planned, it will be those who just missed out from those countries who will take up the redistributed seats.
But in those weeks the European Parliament will be voting on whether to approve the selected president for the European Commission, Europe’s top job.
British Eurosceptics could play a role in blocking someone they particularly don’t like.
All of the European Parliament’s 15 presidents have been white and only two have been women.
While only 20 MEPs in the last legislative term came from a minority background, six were from the UK.
While the turmoil in the British government over Brexit continues, there’s still the chance of a further extension past October 31 – so the British MEPs elected may end up sitting in the Parliament for longer than they expect.
