Hello, sorry I don't have an answer for you, but I would just like to share with you that I'm having the exactly the same problems as you. I also have a peugeot 206 but petrol, It too has been playing up at the moment.
For over a month it now there seems to alot less power when moving off from 1st to 2nd, worse in 2nd. However last week it was terrible as it kept totally loosing its power when I set out. every time when I came to a stop it just give in. It was not the battery either. The power failure lucky was just that day, but still the 1st to 2nd gear low power still remains and it wears you out driving eh? Sorry to jump in on your post but I was just looking through and saw what responses you got and to tell you that you are not alone x