Extending insulated flexible duct?

[Spreadsheetman]

I’ve been doing a “how it works” investigation in the house I have just bought and have found a prime bodge in the en-suite.

 

There is an extractor fan in the ceiling discharging into an insulated flexible duct in the loft. I’d not spotted an outlet anywhere so went looking today and lo and behold, no outlet, the duct was just open to the loft space. It appears that the duct was a little too short and whoever was installing gave up without drilling the gable wall for an outlet and extending the duct.

 

I’m going to sort it with a couple of metres extra duct and I thought to use (say) 200mm of 100mm plastic pipe as a joiner with a couple of jubilee clips to connect the inners, overlap the insulation (25mm glass fibre), pull the outers together and wrap with aluminium tape.

 

Does that sound workable, or is there a more correct way of doing it?
 

(Fortunately the extract fan is broken and the en-suite was hardly ever used, so no damage done in the loft)