Have they a greenhouse? Jade vine, Strongylodon macrobotrys, might be an
interesting choice.
http://www.cambridge2000.com/gallery/html/P3185458.html

Berberidopsis corallina?
http://www.pfaf.org/database/plants....psis+corallina
http://www.bbc.co.uk/gardening/plant...pages/87.shtml

Coral bark Japanese maple? (Acer palmatum 'Sango kaku')
http://www.soonerplantfarm.com/index...plants.plantDe
tail&plant_id=47
http://www.collierarbor.com/aaSpring07.php
http://www.fowa.org.uk/holf61/holf61.htm

I know there are some very good nurseries in Surrey; they should be able
to tell you what might grow well for your parents. I believe most of
Surrey has neutral to slightly basic soils.

Another possibility for an anniversary, though you might have to look
for it in the UK, is Euonymus americana. One of the common names is
"hearts busting with love", or hearts-a-bursting, though probably
better known as American strawberry bush.
http://www.floridata.com/ref/e/euon_ame.cfm

There are also some very nice peonies with "Coral" in the cultivar
name. Peonies are quite hardy and long-lived, so that's another
possibility. e.g.: http://www.thirdbranch.com/pages/peonydivs.html
And there's Paeonia mascula, aka Paeonia corallina, coral peony:
http://www.cambridge2000.com/gallery/html/P4186089.html
http://pages.unibas.ch/botgarten/mit...garten/e.shtml

Kay