Once you've done the groundwork (Stallion's well rehearsed) most of the 'nerves' problems can be put down to physical tension, A set of good simple relaxation exercises can work wonders and can eventually become second nature.
The simple act of dropping your shoulders (a sure sign of tension) and making sure that you are sitting (or standing) comfortably does the trick for me. Can't remember the last time I was nervous (all the other problems that go with singing and getting old are a different matter)
If you're in the vicinity of Will Fly, jump at the chance - he seems to know what he's talking about.
Elsewhere, Sandra Kerr used to do excellent workshops - N.E. England. Have no idea where Frankie Armstrong is, but she also did them (mainly concentrated on voice production), as did Pam Bishop (who was from
Birmingham but I think moved further north). All these names are from the past and may no longer be relevant.
Good luck,
Jim Carroll