Brad Jayakody, 30, said he was passing through security at Heathrow Airport's Terminal 5 for a business trip to Dusseldorf, Germany, when a guard began joking with him about his "Transformers" shirt, which featured main villain Megatron, The Daily Mail reported Monday.

"Then he explains that since Megatron is holding a gun, I'm not allowed to fly," he said.

Jayakody said the guard gave him the option of changing his shirt or facing arrest for the "offensive" image.

"It's a 40-foot tall cartoon robot with a gun as an arm," Jayakody said. "There is no way this shirt is offensive in any way, and what, I'm going to use the shirt to pretend I have a gun?

The passenger said he changed his shirt.

A spokesman for BAA, which runs the airport, said the incident is being investigated.