A photograph speaks a thousand words.... but without one,, do you mean all the branches, including the top? When did the problem start? I'm assuming its in the ground and not a pot, is it in an area of soil that's often very damp or positively wet? Is it planted in a low spot in the garden, or an exposed, windy, cold spot? Was it in a pot before you moved it, or did you move it from the ground to its new place? Was its previous growing position warmer, brighter, or colder and darker? Sorry about all the questions, but for a diagnosis, as much information as possible gives a better chance of an accurate assessment...

You might have damaged the root system in moving it. I hope that wasn't fatal. There is a tap root but the other shallow roots key to the viability of this plant might have been chopped or torn off when moving.

Open position, windy planted directly in ground as was previously. Now quite exposedcwhereas previously it was by a greenhouse, but has been here over two years and fine up until now

If its 6 or 7 inches on every branch, that won't have happened in the last month, it will have started slowly and increased over time. Could be root rot of some sort, or damage to the roots when you moved it and it just hasn't recovered from that very well. If the top branch looks healthy, it may continue to grow, even if the other branches die right back.