He didn't say the 'least racist society', he said 'one of the least racist societies', there is a difference between those two statements. Plus it isn't unreasonable as a statement. Sure you can point to lots of racist parts of UK society, but the UK's population is more diverse than many nations and a diverse population and multiculturalism generally equates a more accepting society in regard to race. It is countries where there is less diversity in the population where they are generally less tolerate of different races. That of course does not mean the UK is any where near where it ideally should be... just more so than many others.