AHi.

I'm attempting to make sugar beer bottles. I'm in the uk so using golden syrup and sugar. So far my first bottle didn't set as it wasn't hot enough. My second melted the jug it was in and burnt So if I'm making the sugar in the microwave how can I tell that its hot enought to harden without letting it burn etc Thanks

You don't make sugar for molding in the microwave.  You need to do it on the stove with a candy thermometer.

You can melt isomalt in the microwave.

"melted the jug"--????

A mold for poured sugar or isomalt would either be hard candy mold [thick white plastic] or silicone.  It would generally be able to handle temps up to 350-400F.  You can't use just any plastic.