Neighbours extractor fan vents into our garden

Sandtree

Bendy_House said:

Regardless, first call up the 'environmental health' or 'nuisance' department of your LA and explain the situation. Also call 'Planning' for ditto. I find it hard to believe this 'conforms'. (whether it's Planning or Build Regs, I don't know - just keep asking to be put through to the other if one says 'Non')

I think this would be considered a statutory nuisance. It's also solvable by the neighbour, either by using a recirculating extractor (not as good) or by venting it upwards through their roof (a bit of cost, but tough).

Meanwhile, no, you cannot/shouldn't touch it.

The OP has already said it is vented vertically from the roof

From what I've seen (eg What is statutory nuisance? | Shropshire Council) domestic cooking rarely falls into the category of nuisance