Hi Pauline,
I'm sorry to say this but it rather looks like they are trying to get you off Byetta, no doubt on the grounds of cost rather than effectiveness. The 5mg pen costs the NHS exactly the same as the 10 pen, so it looks like they are trying to maneouvre themselves into a position where they can either say that it is no longer effective, or that you no longer need it. I'm afraid that all you can do is to go along with their suggestions, but, bearing in mind that the only diabetes medications that do not encourage weight gain are metformin and Byetta, you can justifiably request to go back onto Byetta if your weight starts to increase when they stop the Byetta completely.