No, currently none of the Magnum ice cream products are Halal certified.

According to the official Magnum UK website:

• “Currently, none of our Magnum ice cream products are Halal certified. However, we do work with the GMWA, supplying product information to them, in order for the GMWA to determine whether our products can be consumed by Muslims. This is purely the opinion of the GMWA and not the opinion of Unilever UK and Ireland. We hope that by working with the GMWA Muslim consumers can make an informed decision about our products.”
• Specifically, the Magnum Double Gold Caramel Billionaire is not Halal certified.

Sources:

• Magnum FAQs

Additionally, Magnum is owned by Unilever, a company that has been associated with supporting Israel.

And Allah knows best.