hey ho, Conservatories in the UK are notorious for that nighttime humidity spike. If two dehumidifiers aren't cutting it, your best bet is airflow and temperature.
Make sure you have plenty of fans moving air around the plant itself to prevent "dead spots" where mold loves to start. Also, try to keep the space a bit warmer at night if possible cold air holds less moisture, which pushes the RH up. If the humidity is still stubborn, a bit of light defoliation to thin out the middle of the plant can really help the air circulate better through the buds.
Stay vigilant, you're doing great keeping those buds safe!
Happy Growing, Growmie!