Have you done a test inflation on the spare saver ? I did mine (using the mini compressor in the boot) just in case , it went up fine . I hope never to need it.
I had to use mine one day. With a great deal of trepidation I set off home and whilst I kept the speed down I wouldn't have noticed a difference. Fortunately my tyres (rears!) were spent anyway so no loss.
I did a test inflation, and it did not inflate evenly, the inner wall was still partially compressed.
Deflated it and did it again, this time it inflated evenly.
Thanks for the suggestion Peter, pleased I found that out now, rather than at the side of a wet road, one night!