Thats dangerous, why would you have only back lights on. You're not at all visible from the people who are supposed to be moving out your way, who are notified by the blue lights..
British cars are underpowed light wise. Barely any 360 illumination Example i saw a unmarked car the other with ONLY back blue lights. No lights were visible in the front, it looked normal
Serious injuries? I wouldn't tackle someone if they would have that. He may be a robber but take into account he should at least be considered safety-wise. Perhaps a taser?