envelope for returning ESA 50 too small, question

hello so my time has come for the ESA form to be returned with all my extra evidence.

if I find I cant fit it all in the envelope, are we still okay to just tape their envelope to the front a bigger a4 envelope and send that, as I did last time?

thanks

I'm going to send it next day recorded and pay for the peace of mind, so hopefully that side of things won't be any issue.

I suppose Im actually asking if its fine to send it in another envelope, just it says return in the envelope provided and Im never 100% sure with the DWP if this is an order that must be obeyed or if in this case as long as it arrives there in time to the correct address, its not a problem if you use your own envelope.

small thing I know, but my evidence is a good few sheets and my stomach is in knots about the whole thing anyway and just thought if others had used their own enveloped with no issues, i could at least calm that thought