Thanks for the in depth reply gr5!
I've emailed Ultimaker support regarding the fan, I bought the printer from a third party reseller, so I guess I could always return the unit if we also think the intermittent extrusion problem is a fault. Last resort option though.
I've not changed a thing since getting it - still running default Cura settings (temp etc) and the filament that came with the printer.
Believing the problem to be with the extruder, I have already removed the filament, opened the extruder to check for debris and put it all back together. I also played will the the extruder tension spring settings
I do not believe it to be a problem with a blockage as filament does fall stright down rather than curling.
I will note that my filament is dented after passing through the extruder, however after seeing other threads here, this seems to be very common
I will try the print you linked to in the morning, aswell as placing the filament on the floor - although this is not ideal, I feel that I have spent a fair bit on a premium machine - I'd expect it to atleast work as advertised/intended!