Sounds very strange. The CAA as usual showing they don't know their own rules. But here is a link to the form:
Temporary Certificate of Licence Privileges for Ratings or Certificates
Section 2 includes Multi pilot type ratings. I have issued them and had pilots use them for various types.
But if you have more than 8 weeks between finishing the TR and starting line training you don't need one anyway. 3-4 weeks is usually enough for them to issue it when you send everything by post/courier. Unless they lose it of course...