Stuck for a gift for this couple...

[sparklins]

They are late 40s and have an anniversary coming up soon. Alcohol is a bit of a tricky one as one of them had problems with it (maybe still does).
One is also on a health kick so any hampers with chocolate/treats won't be used.

My budget is around £50 give or take.
I feel really stuck so would really appreciate any input!

Houseplant or tree or shrub for the garden? Voucher for a meal out?

Digital photo frame? Or a photo book with their family pictures, you can include the older ones if you have them and there are programs like Photoglory or Inpaint where you can colorize old photos or make them look newer.

I second getting a voucher for a meal out, too.

Wedding anniversary video that you can burn to DVD or email to them.

Something useful or decorative for their house is probably a safe idea.

Just a gorgeous bunch of flowers or a voucher for their local art house cinema or something similar.

Gift voucher to a restaurant local to them?