Not 100% sure about how you guys do things in the UK, but by what I've heard you have stricter ethics boards than in Canada; and we have strict boards so that's saying something.
While we do have live animal testing they're always under anesthesia (high quality anesthetics at that), so they do not feel pain during any operation. Depending on what is being tested the mouse could experience pain and discomfort later, but it's always minimized as much as possible. Also, if a study requires an animal to experience pain there is usually tough requirements to justify that, and the number of animals tested is minimized.
My experience from a lab newbie to performing surgery was the following:
Pass an ethics examination which required 12hs of lecture
Undergo handling technique training - 2hs lecture, 2hs practical
Undergo surgery training - 2hs lecture, 4hs practical
Perform non-recovery surgery for 6 months (where a mouse that is being sacrificed for another reason, not just for my practice, is sacrificed in a pain-free method)
Performing recovery surgery
So to even touch a mouse or rat you need to have tons of training, as to even inject a mouse with saline solution requires step 1 & 2. To do something that might actually cause pain requires much more training.