Anyone got any ideas how to stop resin being scratched?
I’ve made a few resin tables and the resin can scratch quite easily.
Is there anything that can be applied to help it to be a bit more resistant?

Not really. Realistically, epoxies are normally around an 80 to 85 Shore D, so they are already quite hard. There's not much around that's easy to apply and harder than that. Some automotive/marine topcoats can be quite tough. If you can get hold of a ceramic automotive clear coat, then those are extremely tough and would be the best bet. Extremely expensive though, and would require the ability to heat cure.

Other than that, a piece of custom cut glass over the top would be much tougher.