It needs to go before the trap Tristar.
There are plenty of adpaters to take the Overflow pipe up to 1¼ " or 1 ½"
I was following this advice from Worcester Bosch above:
connecting into the internal discharge branch (e.g. sink
waste or washing machine) with an external termination,
the condensate discharge pipe should have a
minimum diameter of 22 mm with no length restriction
and should incorporate a trap with a 75 mm (3) (built
into the boiler) seal.
The connection should preferably
be made down stream of the sink waste trap. If the
connection is only possible upstream, then an air
break is needed between the two traps. This is normally
provided by the sink waste.