Hi
Although you dont actually need a covering letter for your meds from a doctor only your prescription for each medicine it was the letter that i believe got me the meds as the doctor at Celebration told me alot of people come into her and do what they call DOCTOR SHOP for opiates!!
Luckily the letter i had,had all the fax numbers of the hospital and doc surgery on incase she wanted to verify I had already been to 4 doctors trying to get these meds and all of them said that they could not see me! Even the receptionist at Celebration didnt think i would get the medicine replaced there was no problem with some of the Opiates but 1 type caused me some grief trying to get.
Good advice- Take all contact details for doctors and consultants and always have convering letters.
We were so luckly on one occasion, we were traveling through the night to fly out of MAN the following morning when my dd's insulin pump stopped working. We phoned the helpline number, usa from a mobile

It was now 11.30pm we were still in scotland and knew that we would not be able to continue to travel without another pump. I looked through my phone and by some stroke of luck found a number for the pump rep who had trained us to use the pump 3 years before. I phoned and asked if any spares where stored at any hospitals on route to manchester. She went above and beyond and drove 80 miles to meet us (in bad snow) with another pump. If I hadn't had that number (and she hadn't been so kind )then there was no way we could have gone on holiday. And as by that time it was the middle of the night all I could find to give her was a small bunch flowers and chocs from the service station we were meeting at. As a result I travel with all hospital contact numbers even if just having a break here in the UK.