FlightPath, you are correct that both bits of Doc 4444 apply but I think the OP was asking about WT separation for pairs of departing aircraft using the same runway.
The bit you mention about 'Departures can be 1 min if diverging on 45 degree paths, or 2 mins if the leading ac is faster (or speed controls in place)' is an IFR separation and WT separation minima will have to be applied if that is greater, i.e., if it's a single runway operation, a MEDIUM following a HEAVY will need 2 minutes separation (for WT purposes) regardless of the tracks the aircraft will be following.