Cheers all. Will try all these suggestions. Where can I get these Vocal Zones - in a regular chemist?
It was a sing-yr-own night so I was quite happy to admit to them. I did two sets of two, and in each case it was the second one where I wavered. It could be because the first ones went down well & so I lost confidence in the seconds in case they wouldn't go down so well (perverse but strangely logical). Also I think I didn't collect myself sufficiently to get 'into' the second ones & so I knew they weren't going well & hence the nerves crept in. And once I head myself waver I was lost really - so I suppose I just need a trick that I can believe will get me back on track.
I just tried a good yawn (I'm at work so it didn't feel out of place) and it did seem like it would loosen the thoat so perhaps I'll pin my faith behind that one. Might look a bit odd though !
I'm still new to this, so all this advice is very welcome - so thanks very much everyone.

Kris