I suspect there are some people who use the same word for both, since "syrup" generally can mean "any liquid mostly made of sugar", and so in that sense treacle is a kind of syrup.

But the people I'm talking about call the thing you and I call "(golden) syrup", "treacle", and the thing you and I call "treacle", "black treacle".

This usage has leaked southwards via the fact that neither "treacle sponge" nor "treacle tart" contains anything black: the syrup in them is golden.