Close enough. But dont be tempted to leave it on longer than necessary, or drive at full speed-even though it would probably cope well enough.
Mixing tyres sizes etc on the same axle is technically illegal, In the unlikely event of being stopped by the police you might need to convince them you are being reasonable in using it -" Safer then remaining where I was ," blah blah
. I think space savers used in an emergency are exempt because they are so obviously wrong and have speed limit stickers.
Might be best to leave it at home for an mot test. It would fail if fitted, and might be recorded as an advisory even when not in use.