I went from competitive obedience training to Retriever tests and trials and then onto HPR trials. There isn't much of a change of training needed when moving from competitive obedience to retriever tests , all that is needed is to add some much more difficult retrieves . There is, however, a very big difference between doing either or both obedience and retriever tests and doing an HPR's "proper" work. To do that requires the handler to make a change of his/her own "mind-set." Possibly that is the reason why some very good retriever trainers don't do very well when they try to train an HPR. They fail to recognize that the dog needs to be left with an awful lot more inititiative when it is required to work as an HPR.
To put it crudely, if I was competing in an obedience arena I'd not only expect my dog to sh*t on the shovel to command , I'd expect it to produce the colour I commanded too ! That sort of training would ruin a perfectly good HPR for it's "real" work. At the very least it probably would not hunt well, it would be too handler conscious.....too inhibited....unless it was a bit of a headcase !

Too much strict obedience work takes the "go" out of a dog. The dog would probably become a "ploddy" sort of hunter and not become enough of a free spirit. I find explaining this difficult but I have seen the results of training HPR's ...and spaniels, too much strict obedience first before allowing them to get going as hunters. It can take the "sting" out of a pup to a degree that would make that pup unlikely to win any Hpr tests or trials.
Just my opinion following about 30 years of training HPR's and taking gundog classes for these breeds.
There are some good HPR trainers down in the lower half of England, some have won trials, some have not but they are still good trainers. The two I know personally you would need to travel to. I thoroughly recommend Rory Majors of Bryantscroft Kennels. Rory is not a "One Horse Show." He has made up champions in HPR trials with both G.W.H.P.'s and with Brittanies. He has also done rather well in trials with labs and spaniels. He is a bit like me ....he is a user of more old fashioned methods but you will not find many, if any, good HPR trainers who use only clickers.
The other man I had in mind is Guy Bagshaw. As yet he has still to win a trial but he knows what is needed to win one. I believe he takes training classes in Hampshire and can also provide the absolutely essential birds that need to be shot if a dog is to be trialed.
Your post did not mention your access to suitable hunting grounds with game on the ground ? Retrievers can be trained to a high standard....good enough to win tests, using only dummies but HPR's can not be trained using only dummies. HPR's do not point dummies. They need to hunt for, point on, flush to command live game and then be steady to it. That could involve you in doing a lot of travelling to get to suitable ground for training with game and a LOT more thought and work than is needed for either competitive obedience or for retriever test work...... you have been warned !
Wullie