I'll do a full report, there are some cancellations going on (and more for other airlines too). HAL have put this out:
This was at 11:33
Operational update: Following an improvement in current weather conditions at LHR, the arrivals flow rate (AFR) has been increased to 44/60 as of 11:24 until 14:00.
Current Impact & Actions: Arriving aircraft remain restricted, however an improved flow rate will allow for more aircraft to land each hour.

Risks/Potential impacts: Schedule slippage and slot delays, albeit an improving picture. Any deterioration in the weather conditions may result in a reduced AFR being implemented.
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Then this was at 11:54
Operational update: Due to deteriorating weather conditions at LHR, the arrivals flow rate (AFR) has reduced to 40/60. A band of fog is currently rolling in across the south of the airfield.
Current Impact & Actions: Arriving aircraft remain restricted and slot delays are averaging 30-40mins. NATS and Met Office will continue to monitor the situation closely.

Risks/Potential impacts: Schedule slippage and further cancellations may occur.