I don't know why someone wanting to do some crime needs to clone a plate from the same kind of car. They could stick any old plate on it since it's all checked by automated systems now. The chances of a cop checking it are very slim.
Automated checks do get carried out but the percentage of police cars with ANPR is still very low, there are still lots of vehicle checks done 'manually' by police every day.
The reason they clone a car with a plate matching the correct make, model and colour to the one they are using is precisely so that nothing appears suspicious should a manual check be done, where as if the plate is from a completely different vehicle then the officer conducting the check will know something is up straight away.