If (a) he died in hospital and (b) it was late in the year and the death wasn't registered until 1968 (which could also be the case if there was an inquest), there's a possible death in the Bradford district in the March qtr of 1968.
The GRO index has two entries - Charles Ellis aged 56 and Charley Ellis aged 36, both with the same reference number. Because of the similarity, I suspect it may be a single death, but indexed twice because the clerk was working from an unclear original.
On a quick look I couldn't see a probate entry which might have clarified the situation - but there are pages and pages of Ellises, and I didn't look right through them in case Charles was a middle name.
Arthur