Ok, so I took the measurements properly last night :-) ..and using a 7
metre length of house rather than guessing at 8 and using a span of
80cm for the *opening* (not the length of the lintel) I got 3.44kN on
each end which I guess is more or less 7kN UDL so the corrugated lintel
is within spec. I guess that the point loads of the joists above are
more or less converted to uniform loads by the presence of the
brick/blockwork inbetween them & the lintel. Opening up the span to
1.6m I get a total load of about 18kN.

Now to factor in the full size snooker table going in the room
above.... :-)