Dishwasher overflowing due to water backing up waste pipe

My dishwasher has been persistently overflowing. I presumed there was a problem with the inlet valve until I cut off the water supply and, even with the dishwasher not being used, it continued to overflow. The dishwasher waste pipe is connected to the edge of the u-bend under the sink just as it starts to go up again and water from the sink seems to be going down the diswasher waste pipe instead of the sink waste pipe. Any ideas as to how I can fix this?

Thanks

You must reroute the drain hose from the spigot under the sink.
Route it so that it goes up as high as the underside of the worktop before it goes through the unit to the dishwasher.