No point doing that until you know what happened to this one. It certainly looks rather poorly. Does it have to be in a container? it might be worth lifting it and looking at the roots to see if they are healthy or under attack from something - root mealy bug , vine weevil etc, though it doesn't sound very likely. Have you got drainage holes in the tub? Perhaps it would do better in the ground.

Since it's in a pot check that it's getting enough moisture as it's a fairly fast grower. Lovely shrub though.

How long has it been in the pot?

This could be leaf scorch from too much wind. The older leaves tend to go first. This plant needs to be in a sheltered location. They also don't like prolonged wet & rainy periods. Be sure it has proper drainage and not waterlogged. They are also prone to cold damage if temps go below freezing.

Thanks everyone. In the flightpath at Heathrow we are prone to wind. Maybe I'll take it to the nursery, no wind there.Also, it's been very dry this year, that could be it.
Thanks again for all the advice.

It's the pot - these aren't good subjects for keeping in pots longer than about 18 months.

I can sympathize with you Thorneyside. I live in the flight path to JFK. The pot may be a secondary issue but since we can't see it, that's only a guess. Here is some information you might find helpful.

http://www.gardenseeker.com/shrubs/garrya_elliptica_jan_1st_2001.htm