Finally found what I am looking for after hours on Google.

Just in case anyone else is interested, this is from their web site:

The DVS No-Touch WC Automatic Flushing System is an electronically
operated drop valve which replaces the traditional syphon and delivers
a measured volume of water from the cistern to the lavatory bowl. A
simple wave of a hand pass the fitted sensor will activate the
electronic flushvalve. Fits Existing and New WCs - Installed in
existing and new cisterns using industry standard fittings.

http://www.dartvalley.co.uk/flushing.htm

Apparently there are other manufacturers of these things. I would be
happy to hear from amybody that can track them down.

Tim