Thank you for all your replies - one of the main reasons why I feel I get wrist ache is the nature of my job, I do a lot of typing so I guess that doesn't help matters. I can tell a difference in that when I practice at a weekend, e.g. today, my wrist hasn't ached half as much as it does when I practice in the week, and also I tend to practice more at a weekend!
I bought a thumb rest, which incidentally came today. I tried it out, I couldn't get it in a position that I was majorly comfortable, as each position changed my thumb position and ultimately, it made the flute roll in on me which I have never found to be a problem before! To be honest, I think the flute slipping thing may be the sweat on the lip plate, as on my previous flute, I think it's fully nickel plated (it was a very cheap one so I'm presuming here) and as it was second hand, some of the plating had tarnished and I think it left a bit a of a grip on the lip plate! Is there anything else I can use on the lip plate, I don't want the local newsagents thinking I'm smoking funny things
I have gone back to my old flute, and as I said, I think that the difference in the shape and style of the lip plate is making a difference. I don't want to go back playing my old one really, the last time I tried it, it gave me spots
I am starting to enjoy the tone of my new flute more now - it's just the slipping problem that's getting to me