You should see what the know-it-alls think. A quick recovery coil cylinder can be downsized. This is common knowledge, yet the know-it-alls get out their school physics books and say it doesn't. No experience whatsoever, but boy they know-it-all. I directed them to the Albion web site. They knew more than Albion of course. Even Gledhill say the same.

"CondenCyl HE ’s high efficiency coil and its ability to heat only the water you require means that a smaller capacity cylinder can be used. For example, a typical 120 litre cylinder to meet Part L requirements would reduce to 75 litres using a CondenCyl HE."
http://www.gledhill.net/building-pro.../condencyl.htm

The know-it-alls thread:
http://tinyurl.com/64zql

On one thread one man was limited to space, and they convinced him to go 120 litre when even a 45 litre would have done it. Unbelievable. That is the problem with this mediam, the OPs don't know who is genuine.