Old Unilever preference share certificates

I was sorting though some old papers belonging to my deceased father and found two share certificates for Unilever 7% and 8% Cumulative Preference shares which were bought by my grandfather in 1943. They are stamped on the back 'Probate exhibited 2 July 1965' with my father's name and a registrar's signature, so I imagine my father became the beneficial owner when his father died.
I did some Googling and found an announcement in 2017 that Unilever were buying back their preference shares with the 'settlement of the offer expected in Q4 2017'.  In 2017 my father would not have been capable of following up on this information even if he had known about it which I doubt. 
Given the length of time since that announcement, I wonder if these certficates still have any value.
Can anyone advise?
Many thanks


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