It's wise to carry medicines in your hand luggage just in case your suitcase goes missing - but you could split it if there are large bottles. Morphine/Oramorph is a 'controlled' drug so yes, you need to take certain information with you, your prescription alone won't be enough. Make sure it's in the original packaging (as with any prescription medication - makes it easier to see what it is. Then, for any controlled drugs, get a letter from your GP with all your details (name, address, DOB etc), where you're going (all places if travelling around), dates of travel and the details of the medication. The letter needs to state what it is, total amount you'd be carrying into the country, usual dosage etc - and ensure it lists all 'controlled' meds. You don't have to do this for just usual prescription medications.
Just make sure you allow time to get the letter done. I would hope the GP wouldn't charge for writing it but they may