Sustrans (Sustainable Transport) http://www.sustrans.org.uk/ say:
"Anything more obstructive than bollards is inconvenient to ordinary cyclists and may be totally impassable for those with trailers for shopping or children, tandems, especially if loaded, recumbents and any other non-conventional bike. Access controls frequently inhibit the use of a path by many disabled people especially those using any form of wheeled vehicle apart from a conventional pushed wheelchair. Indeed, in the words of one path manager,
‘Access controls stop the very people we want to use paths the most’."
The Pedestrians' Association http://www.livingstreets.org.uk/ also say:
"Guard-railing spoils the look of many of our streets, as well as making it more difficult to cross the road."