Parents who have to be pursued through the courts or have child maintenance payments deducted from their wages will risk a charge of £300 under a new child support system that comes into force today.
Parents will also face fees if they cannot come to an amicable arrangement on supporting their children financially.
The new system means the Child Support Agency (CSA) will be phased out over the next three years and replaced with the Child Maintenance Service (CMS).
Letters have already been sent to 50,000 parents in England, Scotland and Wales earlier this year warning them of the changes.
More top news
Police have launched an investigation after a woman found a hidden camera while in the shower at a Travelodge.
A plumber who virtually decapitated his girlfriend with a breadknife has avoided a murder trial - because he is an alcoholic.
A man who opened a parcel addressed to his new home was shocked to discover a large tarantula inside.