For many motorists their cars are their pride and joy. This leads to some car owners making changes to their vehicles in order to make them more personalised – a process which is known as modifying.

Modifications can include fitting a vehicle with different wheels, painting it a different colour or pattern and even switching the colour of the car's windows.

However, there are restrictions to what motorists can modify. For instance in the UK, vehicles are not allowed blacked out windows and as of last month in Peoria, Illinois, police are now allowed to fine both drivers of vehicles with tinted windows and also window tinting companies who carry out the work.

Aside from legal considerations, motorists should also be aware that making changes to their vehicles could modify the price of their car insurance premiums.

In March this year, the Insurance Daily reported that modifying a vehicle can increase a car premium by as much as 139 per cent, the equivalent to an average of £545.

Furthermore, the website reports that modifications can render an insurance policy invalid if the motorist does not inform their broker of the changes that have been made.

Jennifer Culley, spokesperson for Direct Line Car Insurance, said: "Generally, any modifications to your car that increase the performance, value or its desirability to a thief will attract increased premiums as they may raise the risk, value or likelihood of a claim."

However, she did explain that insurers will not "generally penalise a customer for modifications that make [a] car safer or lower the risk of damage or theft".

The bug bear is that many modifications have negative safety implications. For example, in May 2007 the European Union banned bull bars on 4x4 vehicles in a bid to cut the number of deaths and serious injuries they cause.

A new law was passed which effectively banned popular bull bars in the UK.

Direct Line Car Insurance also advises that a professional should undertake modifications that are made as there may be safety implications, which a typical motorist might not be aware of.

Furthermore, car owners should notify their insurers of the change before it is made rather than afterwards so that they will know how the modification will affect their premium.

"Once the modifications have been fitted, make sure they are noted on your policy to ensure you have the cover you need and you are not invalidating your policy," said Ms Culley.

Motorists were also told to read up on the law on modifications and make sure they are aware that tinted windows must allow a minimum of 70 per cent light through, for example.

Furthermore, personalised number plates are required to adhere to the DVLA's formats and fonts and a failure to do so could lead to prosecution.

Ms Culley concluded that it is essential for drivers to know this as if they break these regulations then brokers will not insure their vehicles.