Nothing. It will re-shoot from buds just below the damaged shoots.

Exactly the same thing happened to ours this year. I did read some advice that to help avoid frost damage you should keep it sheltered from the east and also the morning sun.

I'm going to try placing a hurdle to protect ours this coming winter/early spring and be on standby with a bit of fleece.

I did read that it's perfectly acceptable to prune away frost damaged growth and dead-head the flowers in late Spring, but take great care not to damage the new buds as Fractal describes above (cosmeticly it makes a big improvement). I did this to ours a few days ago, She looks better already.

Fractal and Mrv - many thanks - sounds like good advice will go out now and do it.

You're welcome :)