If you're from the UK, you probably already know this, but just in case:
1) Britain (like most of the rest of the world) runs on 240V, so MAKE SURE your nebulizer runs on 240V. One time in India I plugged in my 120V nebulizer (not realizing the difference between 240V and 120V) and it overloaded and died. If you don't have a 240V nebulizer, then either get one (one that runs on both 240V and 120V so you can use it in both the US and Europe), or buy a 120V to 240V voltage converter, or "step-up". It may be cheaper to buy one in the UK. But step-ups overheat easily and usually die within a few weeks if you use them regularly. The Vest already runs on 240/120V, so no need to worry about that.
2) Make sure you have UK plug adaptors for your other electronics.
3) make sure to put your refrigerated meds on ice-packs in an insulated lunch box. If the ice packs lose their cool, ask the flight attendant for ice to fill up your lunch box. They usually can do that for you. You might want to bring a zip lock with you to put the ice in. But ice packs should keep cool for 8 hours, I think. There is a difference between the amount of time Tobi and pulmozyme can be unrefrigerated (or out of a cool environment). Pulmozyme can be out of the fridge for up to 24 hours I think, but Tobi is more finicky. Check with your pharmacist.