Some questions for you in order to determine what the problem might be - 1, is the Choisya in the ground or in a pot, 2, how long has it been planted, 3, what part of the country are you in?

The choisya is 2 yrs old in a good size pot and we live in thye Manchester area. I,m thankful for any help.

Right, its in a pot, I wondered, because it sounds like its suffering from drought - if you've had reasonable weather in the last 3 or 4 weeks, with or without rain, and the plant is standing in sun, that could be what it is. Otherwise, check whether its potbound, and whether there's any indication of invaders in the pot/compost, such as vine weevil.

Dear bamboo,
Thankyou for your advice, and we take the advice and act upon it and let you know.