The 8L/min I can believe, but at 0.1 bar sounds a bit unlikely. At 1 bar
it may be right.

Thought it sounded a little suspect...

While i'm at it, how the hell do you figure out what your pressure is?
If you really want to know, something like:
http://www.screwfix.com/prods/82412/...ure-Test-Gauge
Not that it tells you much of interest usually.

Given that i'm only likely to be using it the once, hardly seems worth
it :-}

Not really. There is also a difference in the flow rate the main will
supply (probably well in excess of 9 lpm), and that which the boiler can
heat to a reasonable level.

I'd hazard a wild guess at saying the cold water can deliver at LEAST
twice as much per minute than the hot, perhaps as much as four times
(without getting jugs out of the cupboard to measure it)

I've tried to play safe when ordering taps for the bath / sink by
going for 0.2bar jobbies, but I don't know how low I should be setting
my sights at for a shower mixer valve (i.e. would a 0.5bar be ok ?)
Chances are you have mains pressure of at least 1 bar.

....wonder how well one of the large shower heads will cope... missus
likes them...

With a combi the pressure should be equal (roughly) anyway.

Nah, nowhere near - either that, or i'm confusing pressure with flow
rate again - it's a downstairs bathroom, and the main comes in about 6
feet from the bath taps, and the cold tap is plumbed direct to it
(give or take a tee for basin and bog) - the boiler is almost directly
above, but on the first floor.

Some wax capsule types allow hot to flow until the output mix reaches a
limit temperature, and then they progressively constrict the flow of the
hot. The valve normally being such that you can't select just hot - you
must also have some cold. Hence throttling the hot supply cools the mix.

I would have thought it'd go the other way around - it'd let the hot
flow at full force, and the cold would be adjusted to keep within the
temperature range.

A mixer that responds to a rise in temp by increasing the cold flow rate
works better in these cases.

Aha - I think that's what I was babbling on about in the previous
sentence - any ideas how you can tell one from the other ?