Now I have replaced mine with a Powerspark one and was using a blue 3mm silicone hose, which I think started to deteriorate and collapse under vacuum after the constant motorway run. This was further proved after I changed the hose with new (same spare hose) and the symptoms stopped immediately.
So, to stop this possibly happening again, I've now bought some 4mm hose from Powerspark which is constructed using a high quality silicone Polyester or Nomex compound. It is also further reinforced with a polyester layer to provide a more rigid structure to prevent collapse under high Vacuum conditions whilst sustaining pressure.
