The heavy fermion material UPt3 may justly be considered a paradigm for unconventional superconductivity and it remains the best established case of a a bulk, odd-parity, spin triplet superconductor. However, key questions remain unanswered concerning the order parameter of UPt3 in the three different superconducting phases.Here we focus on the vortex lattice (VL) in the so-called B-phase (low-temperature/low-field) and how this will be affected by a possible broken time-reversal symmetry. Our preliminary SANS measurements show a clear indication of a chiral effect on the VL in the B-phase that depends sensitively on the field/temperature history. We propose to continue these measurements and definitively establish the precise connections between the VL structure and a chiral state.