Golden Syrup best before date
A best before date does not specify how long a food item will last. It merely gives a time frame within which an optimum quality can be assumed ( as given by the manufacturer).

Food does not automatically spoil after the best before date, so use common sense.

My gut feeling with golden syrup would be that it's fine unless a change in smell, consistency, color.... can be noticed. That stuff is so high in sugar, that bacteria would really have a hard time there. At my last move, I unearthed a few forgotten bottles of elderberry blossom syrup from (I'd better not tell here), that are still perfectly fine... I tried.

But: If you are planning to serve your syrup outside your family, that is, to kids that aren't your kids, other rules concerning food safety may apply. Check with your local authorities or play it safe and get a new bottle.