You're laughing then. Run in whatever way the plumbing works best. Ensure
there is a direct unvalved path from boiler output to vent and a direct
unvalved path from water inlet to boiler return.

I still reckon gravity with control is the way to go. as we do not have a
problem with HW recovery time and it is a lot simpler to fit.

Then place pumps and valves where appropriate. You can share valves or use
separate as you wish. You can run each of the 28mm or 22mm system as your
desire. Pumps don't count as valves if in the water inlet path. A fixed
(non automatic i.e. gate) bypass valve counts as a path for the water inlet
If the boiler has an additional manual reset overheat cutout, then the
water inlet restrictions can be ignored. The water inlet could even be
combined with the vent under these circumstances, which eliminates pumping
over.

The boiler is fitted with a manual reset overheat cutout, does this mean
that the 2port could be fitted in the HW circuit close to the boiler? The
vent would still have an open path - and the feed have the 2 port valve
inline but would still be in the HW circuit and stop circulation.. This
contradicts what set square recommened which was to fit a "2-port valve in
the HW circuit right next to the cylinder, *after* the vent pipe tee - so as
to maintain an un-interrupted path from the boiler to the vent pipe" whilst
this has the benefit of leaving the feed and vent open at all time - the
ability to stick the valve in the feed/HW circuit close to the boiler would
mean that I could use a RF tank stat
(http://www.screwfix.com/app/sfd/cat/...30214&ts=48069) and save
running a cable to the loft making fitting extremly simple.