Fitting cat flap

[Cocopogo]

I want to put a cat flap in my patio door glass. Who do I get to fit it?

A window installer.

Sounds expensive!

It's not cheap if double glazed.
We have one in the bottom half of our kitchen door. Man had to order a new window panel with the right size hole already cut in and sealed so as not to compromise the double glazing seal. Then fitting the cat flap was easy.
We have kept the old, intact bottom half of the door so we can replace it and take the cat flap if we ever move.
A local window installer did it for us.

It might be cheaper to get an insert (I’ve seen others, this is just an example). It would also stop future buyers without cats being put off.

https://www.amazon.co.uk/PetSafe-Sliding-Glass-Door-Small/dp/B00WFKJWSO/ref=asc_df_B00WFKJWSO/?tag=googshopuk-21&linkCode=df0&hvadid=226613890277&hvpos=&hvnetw=g&hvrand=12242287175389662580&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9045255&hvtargid=pla-349617984409&th=1