Telling car insurance about modifications and consequences?

hi all i i have a ford fiesta xr2i car and the car is originally standard the only thing i have done to it is put a pipercross air filter on it..(direct replacement to my old filter) but i didnt tell my insurance as i wasnt sure if it would shoot up... well anyways the police was doing regular car checks in the city centre tonight and i happend to be one of them lol.... but everything seemed ok until he checked under my bonnet and looked at the air filter(pipercross) !! and also he commented about the 15"alloys on my car (which if i remember rightly this car comes with them exact alloys when bought new )<<<--- anyone know if they do 100%?? its the ford fiesta xr2i 1.8 16v d.o.h.c...... well he took 2 photos with his camera of each.. then he said ok well i have to go!! the other officer is going to give you a fixed ticket for a faulty headlight....so what is the consequences of me not telling insurance about the air filter ?? is this only a problem if i am in any serious crash or summin