Yup, definitely a scam. Created a second a/c in my Mycelium, used that. Interesting that the address is verified first - I deliberately put in a typo, and it came up with an address validation error. When I corrected the address, the following came up ...

"You can withdraw your funds only on external address, which is registered and verified with your account. To verify your (external) address with your account, you need to make a deposit from this address. Deposited amount will be added to your current balance amount and will be available for withdrawal at any time immediately. More information you will find on Deposit area in your profile. Minimal amount of the deposit is 0.01 BTC. Current deposit status: 0 / 0.01 BTC. "

Which of course I have no intention of  doing.

So, yup, looked like it was indeed too good to be true.

Thanks very much everyone.