Someone's up early
I think the filter could be overated (volume of water/pump etc rather than reputation) by Hozelock's specifications, as I'm using the pump they recommended (Titan 3000) with the hose tail cut to 38mm, and there is no choice for the outlet anyway, as it's a 40mm pipe which is going directly into the pond.
According to the OP they told him it's possible that the box had warped, so I'd like to see what they advise.
This is by no means an attack on Hozelock, as all my pond stuff, Titan 2000, Titan 3000, Bioforce 2200UV (electrics died after six years - can't say that's not great service !), Bioforce 4500UV, and a Cascade 3000, is/have been great, as is their staff and service. They are a company who stand by their warranties, as I know, having had stuff replaced very quickly.
Of course I checked everything as I always do when I have had a problem with the ponds (which touch wood, has been very seldom over the six years I've had them)before I blamed the filter.
You have made assumptions about the filter without checking. This is the pump Hozelock want customers to use with the filter. The pump's hosetail is 38mm, the maximum on it. Again recommended by Hozelock. The filter is about 2" above the pond....look, I've read the manual.
The previous filter system (Titan 3000, Bioforce 4500UV had been in place for about four years with no problems)
Do you speak for the makers themselves ?
You obviously assumed it was my fault, and this could just go around in circles, so I'll leave it here.
Peter