Having checked every UK No1 of the 1960s (from all the main magazines), I have a list here of those that were only issued on 78rpm in other countries. Nearly 100. Most of them seem to have been available on 78 somewhere into 1962. There are only a few missing from 1961 (the Temperance Seven's You're Driving Me Crazy, Petula Clark's Sailor, Shirley Bassey's Reach For the Stars / Climb Ev'ry Mountain, Frankie Vaughan's Tower of Strength). From 1963, they become much less common, with The Beatles being outliers. It was largely big name artists like them, Cliff Richard and Elvis Presley whose singles were being released on 78 around the world. The last confirmed ones are from 1965 (I don't believe Elvis Presley's Wooden Heart was issued in 1966): three by The Beatles and one by Cliff, all Indian.
Following the demise of the 78rpm format in the UK, the big hits of the day were generally released in South Africa (into 1962) and India. Other countries pressing Western pop music on 78 were Brazil, the Philippines, Argentina, Colombia and Pakistan. So the main markets for these records were the Indian subcontinent, South Asia, the Far East and South America. If these No1 hits weren't already listed here, I searched Popsike. If it isn't here or there, chances are slim it was issued on 78, I'd say. But who knows.
Oh... I believe one has been passed over...
Dave Clark Five.. "Can't You See That She's Mine" b/w "Because".. an EMI Columbia pressing from India. Not sure if it hit #1 in the UK, but it was a hit. I'd seen something on it on The Beatles "Ticket To Ride" Indian 78 listing...
Yes, it was a hit in the UK, but only reached #10 in the Record Retailer chart - certainly not #1 on any UK chart (there was no “official” listing until 1969). So it doesn’t qualify for the list.
The list now has 100 records. I haven’t added any new titles as such, but I found some foreign issues I didn’t know about before (Cliff Richard in Turkey and Pakistan).