EESDL
Your Battersea example: no prob in 355N.
Say EOW 1670 kg (IFR but no floats), 90 mins fuel at 3kg/min = 270 kg, say 20% reserve = 40 mins x 3 kg = 120 kg, say 5 pax x 90kg = 450 kg. Total weight 2510kg, max Group A TOW 2540 kg.
Don't know about 135 but would guess would do it too.