They had a falling out some time in the past. I don't know the details but I believe it involved Hattons commissioning a product from Bachmann. This sort of thing is relatively common with larger UK model shops, including the occasional bad blood. For example, Rails of Sheffield has a similar situation with Hornby, and doesn't currently do business with them. But that I think has more to do with Hornby's sketchy business strategies that of recently are trying to cut out 3rd party retailers and sell to customers directly/exclusively wherever they can.
I often feel that the model rail industry in the UK definitely hasn't matured as much as it has in North America.