There's a 1mW power limit on laser pointers available for sale in the UK (and most of Europe).
Up to about 5mW is fairly safe as far as eye damage is concerned, at least for the red ones.
It's easy to order fairly high powered green laser pointers (100mW) from foreign parts via the interweb, and the chances of you getting found out are minimal.
Most people who have been prosecuted for using them were pointing them at aircraft (
police helicopters etc), and were done for "recklessly endangering an aircraft". The law has since been amended to allow prosecution for "shining a light at an aircraft in flight so as to dazzle the pilot".
For cars (or anyone else) I doubt there is anything specific - common assault?