ive had the same problem with my rosemary, im still none the wiser why it happened

Hello Hijuiu, I've been putting it down to frost damage as it was perfectly ok last year. It looks really odd from the front!

You should remove all dead growth back to live wood -if the resulting shape is awful, wait till the flowers have faded and trim back the rest to try to get a better shape, but don't take off any more than you have to.

Thanks for that Bamboo. Does that mean there's still hope for it? I keep meaning to scrape at the stem to check for green stuff but haven't done it yet.

The plant is divided at the foot into two main stems. One stem has the brown growth and the other has the live growth.

Well your ceanothus is clearly alive, its flowering - just that one bit's died off, so cut that bit out.

Ceanothus is a funny old shrub, we are on our 4th one. They do well for a while, then this sort of thing happens. The same thing happened to our 2nd one as your shrub. Then another bit went brown, so we took it out, and grew a third really large one, that got rocked in a gale and slowly failed.

They're not long lived shrubs, that's for sure.

Thanks everyone for your suggestions. Looking at the picture (why is it easier to see things in a pic?) I think I'll wait till it finished flowering, cut down the brown bit as it's the whole stem down to the base then reshape the bit that's left as suggested by Bamboo. At least I'll feel as if I'm giving it a chance and if it looks too stupid, it'll have to go!