Hi, welcome to GoY, Prunus laurocerasus are pretty tough plants, and not usually bothered by pests, but they are susceptible to attack by leaf mining moths, so this could be a larvae sack, the best way to know for sure, is to get a knife and cut it open to see what's inside, it's certainly not a beneficial anything, Derek.

Hi Derek,

Thanks very much for the welcome and the answer. I've looked for images of the leaf mining moth pupa and saw one photo that looked a little bit like 'my growth' (-; I can't cut it open as I found the growth in January and put the leaf somewhere 'safe' in the garden and it's long blown away. I would never have cut the branch if I'd seen the growth--I would have just left nature to get on with it. I'm a science tech and I was cutting laurel to take into college for a respiration expt. It was a cold Sunday afternoon in Jan. and I didn't notice the growth till I'd taken all the cut material inside and was about to put the branches in water to keep them fresh till I took them into work the next day. I have so much laurel that I wouldn't mind some of it being used as a breeding ground for some moths (-; Thanks again, Lesley