C. salignus - but it has small yellow flowers. Will survive most of our winters (though probably not last year's). Otherwise, C. citrinus 'Splendens' is hardy in a south facing, very sheltered situation in the south and west - mine survived this year on a southfacing balcony, for instance.

Callistemon linearis is pretty tough - I've had it for 15 years now. The foliage looks very scorched at present but I think it's going to pull through

Many thanks for your replies. Another question, this time on soil. I was going to put a callistemon by a brick wall but is the cement from the wall likely to make to soil alkaline? can you add anything to the soil to ensure it is acidic?

they're usually planted in the lee of a wall or fence for protection, but should be a minimum of 1.5 feet away. I don't think it'll cause any problems with alkalinity - callistemon prefer slightly acid, but its not critical.

When planting Callistemons in our highly alkaline soil, we put in about 1/8 liter of soil sulfur crystals, in an extra wide planting hole. Each crystal forms a zone of acid soil around it that the roots can draw nutrients from.