The DVD is aimed at teaching you the routes, not the RT. It is advisable to do the London heliroutes with an instructor/commercial pilot who is VERY experienced with the procedures before you attempt them yourself.[a commercial pilot from up north was about to take one of their students along the routes and had a frequency that was 4yrs out of date!] Any of the airfields close to London should have someone who can go with you who knows the ropes . The DVD shows you the actual landmarks to look out for, so you have some idea of the route features.
The RT you should already know, but you do need to respond to calls immediately and read back all the instructions you are given, it wouldn't hurt to read through CAP413 again.