I was refused boarding again recently but because I now know the law I jammed the door open and told him that I won't move until he let me on. I quoted the law below and he gave up and cleared the wheelchair space for me.
"S24 of the Public Passenger Vehicle Act 1981 states
Bus drivers refusing to allow wheelchair users onto buses where the wheelchair space is either unoccupied or occupied by people who can readily and reasonably move are committing a crime. They can be prosecuted, given a £500 fine and 3 penalty points."