Owning a laser pen is not an offence, they are generally used by lecturers to highlight points when making a presentation. The vast majority of shop-bought laser pens will be relatively weak; meaning that exposure to the beam of such products would not result in an eye injury.
The website in 'Related Information' explains the different classes of lasers; classification based upon the power of the laser in question. The Health Protection Agency suggests that no laser pens more powerful than Class 2 be available for general sale, due to their potential to cause injury.
Whilst owning a laser pen is not illegal if a person had one in the street and was using it (or intending to use it) to shine in people's eyes, at cars or aircraft etc. then they would be committing an offence and, in the case of cars and aircraft, a particularly serious offence. They may also be personally liable to a Community Protection Notice for anti social behaviour, namely unreasonable behaviour of a persistent or continuing nature which has a detrimental effect on the quality of life of those in the locality.