Terrain Effects Chart for ford area states:
British 1 MP and commandos 1 area to enter. Only 2 units may enter or cross per turn. Only 1 unit may remain in the area at the end of a movement segment. Batteries, disrupted and suppressed may not enter.
Drift and Bridge Areas rules under 6.1 British Movement Segment also mention British units, Commando units and just units.
So, unless side specified, any mention of units applies to both sides. Thus
British may not move to a drift area occupied by a Boer unit in view to assault it due to above rules.