The Foreign Minister has said
that in the event of a no-deal Brexit UK citizens who already have some form of residence permit/certificate will need to exchange it for the biometric residence card in January 2020. If the Withdrawal Agreement is approved the same will apply but the timescale may be different. Click on the down arrow next to "Will it be necessary for British nationals to obtain a residence permit? What will be the steps to take to obtain a residence permit?" on the web page linked above.
It should also act as an identity card which would be better than having to carry your passport everywhere.
PS Whenever you access ekathimerini it always shows today's date in the banner but every article shows the date it was published in the header of that article.