As you will have gathered from the previous replies the Smiths clocks, which were fine in their day, generally haven’t stood the test of time at all well. As I understand it they rely on a electrical contact being made by the balance wheel to energise a small electromagnet that drives the clock. Not surprisingly that mechanical electrical contact tends to fail eventually as it’s been activated with every tick of the clock whilst it was working. That’s an awful lot of ticks over 50 plus years. Moreover each tick causes a tiny arc across the contact which also doesn’t contribute to longevity
You should perhaps hold a little celebration that your clock is working at all - no make it a big celebration!, it’s a rare bit of kit if it’s still working at all. Presuming that it is indeed the original clock it’s relatively easy to adjust in that there is a small screw head on the front which may even still have the original + - marks on it to indicate which way you should turn it to cause the clock to run faster or slower. From memory I
think one turns it clockwise to slow the clock, but I’m really not sure on this point. Never turn the screw by more than about an eight of a turn at a time, then leave well alone for 24 hours and check out success or failure.
Those who have one of the always right twice a day clocks may care to take a look at
https://www.clocks4classics.com/ These clever people have developed an electronic optical sensor to replace the electromechanical contact. I see they offer a kit, which looks incredibly fiddly, or they’ll do it for you.