Thanks guys.

For the record, here is Vaillaints response:

"
If your requirement is for connection to a house soil and vent stack,
British Standard 6798:2000 gives this as a preferred method.

1) Internal termination to internal stack

The condensate drainage pipe should have a minimum diameter of 22mm with no
length restriction. It should incorporate a trap with a 75mm condensate seal
and be connected to the stack at a point at least 450mm above the invert of
the stack.

The condensate is acidic but not acid, in the normal course of events
liquids of an equal or great acidity are routinely poured down a sink or
toilet. The level is about the level of fruit juice or cola type drinks and
while not that palatable would not be considered hazardous if drunk. The
maximum condensate is only 2.2l/h but in normal practice will be much less
due to modulation of heat output. Therefore the connection between the
boiler outlet and stack pipe should be a form of plastic pipe not copper
pipe, once at the stack pipe and therefore into part of the normal drainage
system no restriction is put on the stack pipe material. So the installer is
half right in that the connection from the boiler should be in some form of
plastic but there is no such restriction in the stack pipe material. I am
surprised CORGI expressed any view on this matter as they normally refer
these matters to the manufacturer concerned as this is not directly to do
with gas safety.

I trust this is of some help.

"

I think I will go for the condisating boiler.

Thanks