Well don't know what I was worrying about.
All 5 went in easy as. Could have fit another one or two in.
I just checked how well the 245/75R17 fits in the spare wheel well. It doesn't.
I deflated it, and I cut the carpet back so it wouldn't get caught between tyre and car, and then pushed it in. Stopped a couple of inches short of being fully in. Then I had to get it out! Ended up putting a strap around the inner and levering it out with a timber stud. I've got the start of a rear storage idea in my head where it won't matter if the tyre sits up a bit and will look at that soon.
Thanks for the input guys.