Well, won't say no. As long as I can have plenty of steam to hide the wobbly bits (mine not his) in case the diet has not worked by time of filming
The special goes like this : Authorities become alerted to the abnormal amounts of heat being generated in the Sherwood Forest area. They suspect a huge drugs factory with enough capacity to supply half the galaxy, or other dire threat to the UK --you will have to supply the true reason, I can't think of one.
Obviously Thames House has to send in one of their top agents to investigate ...
So you could save on fees by using one actor for two parts, if you so desired. Double exposure can't be bad