A bike insurance company has urged bikers to declare any modifications they have on their transport, otherwise their policy could become invalid.

The insurer has revealed that exhausts are the most popular modification made to bikes and, if they are performance enhancing, such a change could inflict a higher premium.

Changes to bike's suspension and wheels, increasing capacity over 5 per cent, along with custom motorcycles can all affect a bike insurance policy.

Anthony Aronin, the head of Swinton Bikes, said: "Bikers planning on modifying their motorbikes should always notify their insurer prior to the modification so they know exactly how much it will impact on their bike insurance premium.

"We would also advise riders protect their motor bike with a lock or tracker device which can actually reduce bike insurance quotes and premiums."

However, some modifications hardly affect the premium price. Non-performance enhancing end-cans, crash bars, huggers, crash mushrooms, up-rated braking systems and a 5 per cent increase in engine capacity all have little effect on a policy.