I don't think one would confuse that with a Dak. AN-12s are usually up around FL200+ and sound very heavy.
True, but these days there aren't too many large prop aircraft flying over the UK, so the possible candidates are few. Depending on where in 'The garden of England' the OP was could indicate if it was inbound or outbound from Manston or perhaps Sarfend, especially if it was relatively low. What else flies over ? Hercules, Transall, and the Russians ? If it was a Dak might it have been one of the pollution control examples or are they all gone now ? I can't imagine that too many old vintage planes would be flying around at night without a good reason.
SHJ