Something i've learned (and i've been in exactly the same poistion as you Kirsty, in fact i've been obese all my life) is that your head really needs to be in it.
If you're doing this to satisfy other people, you're really not doing it for the right reasons. You need to be loosing weight for YOU. Don't listen to anyone - if you're ready to do this, then do it for you.
People can help you and give you all the support you need, but you need to be in the right frame of mind. Once you have that sorted, you'll find it easy to refuse those treats in lunch break.
What i would suggest is that you really figure out what you want, and then decide how you want to reach that goal.