Are Bull Bars Legal in the UK?

Why?

Bull bars became a safety issue because a rigid steel bar concentrates the force of a collision onto a pedestrian instead of letting the car's designed crumple structure absorb it. Because of that, frontal protection systems on newer vehicles have to meet a pedestrian-protection approval, and rigid non-approved bars do not.

Beyond the specific approval, there is the general rule that nothing fitted to a vehicle may make it a danger to other road users. A hard, protruding bar fails that test, which is why fitting a traditional bull bar to a road car is treated as making it unroadworthy.

Some soft or approved "A-bars" and styling bars are made to comply, but the heavy tubular bars sold for the look are aimed at off-road or private use. On the road, assume a rigid bull bar is not legal unless it clearly carries the correct pedestrian-safety approval.