My Pests and Diseases book says the cause may be fungal or bacterial infection including bacterial canker, and then rather unhelpfully says determine the primary cause and then take appropriate action.

https://www.rhs.org.uk/advice/profile?PID=86 should help you to find out whether its bacterial canker for starters.

Sorry that's the best I can do - hope someone else will know more.

Shot holes seem to occur on laurels and photinias quite often. It's not too worrying as long as you don't lose all the leaves. If the tree is not too big, then you could use a fungicide but a feed and mulch should keep it going. As far as bacterial canker is concerned, are there any oozing, thick, glue-like substances coming from the trunk or actually dying branches? If this isn't the case, then it's just shot holes you have to contend with.

Thank you both.

Kal