Genuinely upset at this wildflower destruction

It doesn’t sound like there was malice on the part of the neighbours so I don’t think a confrontation would help.
There’s a fairly recent Monty Don series on British gardens where the Northern Ireland episode features a similar alley and all the neighbours have got together to make it ‘wildflower alley’. It was really lovely so I’d use it firstly for ideas on how your stretch of the alley can be made to look more purposeful and less likely to be helpfully cleared. Secondly use as a talking point to explain to the neighbours. My approach would be to actually thank them for their clearing up and say it’s given you a blank canvas to get started.

like this 😊

Thinking about this... I'd be worried they are going for a land grab to extend their garden.

Stake your claim to your "half"

Where do you put your bins ??? (Misses point )

In that case, plant some wild flowers in pots.

On gardeners world you often see these little back access lanes have been officially claimed by the residents, vehicle access blocked by the council (bollards) and legitimately turned into 'flowering ally ways'.

All sorts of weird and wonderful things used as containers and climbers planted on the garden side allowed to sprawl over simple wooden arches across the alley ect.
Plus a good few flower murals 😊🌺🌸💐
Perhaps if there's enough interest from the neighbours you could initiate this? It tends to only need a couple of enthusiastic neighbours at the beginning and enough 'don't minders and won't objectors' to get these things off the ground.

Most folks these days don't have the interest or headspace to actively object to anything and once it's off the ground a good few will see how lovely it is be inspired and join in 🤞

I'd cheerfully include the neighbours who cut down the weeds as if it hadn't happened.

Cow parsley is still flowering here in Kent, and it's massive this year because of the weather conditions.

It's a Sussex word 😀

Rhs 2 to 4 ft but op doesn't know her cow parsley range so it's probably not cow parsley.

@pelargoniums

Op hemlock can also cause serious illness and it's a grey area I've fallen into it also in my garden I used to think it's all cow parsley but it's not.

It's extremely toxic and dangerous hemlock or giant hog weed.

Cow parsley can get to 5 feet, so it might not be hog weed - which you'd probably know by the smell anyway. I'm not a fan in the garden personally cow parsley tends to completely take over and shade out everything else - so your neighbours probably thought they were doing you a favour - anyway let me tell you it'll be all back next year anyway given half a chance! I've been trying to get rid of the stuff for years. The bluebells will also be back regardless.

Anyway OP why not take advantage of this and use it to plant some really beautiful wild flowers. I'd give wild flower mixes (and especially corn poppies/corn flowers) a miss as they're annuals/contain a lot of annuals and unless the ground is disturbed each year the pretty ones often won't come back.

Instead perhaps consider ox eye daisies, scabiousa, knautea macednonica, knapweed and musk mallow. They're all really pretty, can be grown pretty easily from seed, are great for a wild meadow style garden (all quite tall), can compete with grass and will come back year after year.

i think it is going to take a LOT to convince people that perfectly manicured lawns and concrete gardens should be a thing of the past, save the bees

were there nettles there?
so many people are dreadful at destroying wild flowers weeds
what a shame

Quite possibly Hemlock - if it’s in flower now and 6ft. Cow parsley flowers much earlier.
purple blotches on main stem and much stronger growth.
Hemlock is much worse than hogweed if you’re worried about toxicity.

Annoying about the flowers though Op - maybe take the chance to plant something tough/cheap. Comfrey will grow anywhere, loved by bees and will make a green carpet.

What you call wildflowers they probably saw as weeds, and I imagine they thought it was their duty to do the weeding in the bit of lane outside their house.

Maybe just let them know you love it left wild and see if they’d be happy to let it grow back.

You got me at twitten. Had to Google that word! That's my word of the week now - twitten.

Right, back to the OP...

Sorry op cow parsley doesn't grow to six foot and also cow parsley has another close relative hemlock.

Firstly, is any of it your land? Because that may affect how firceful you can be.

Approach.

• either ring their bell and ask politely why they did it. There are some very ignorant people who may have assumed it was just a load of weeds that need tidying (I know!). You can then respond that it was intentionally planted and the cats are now toileting.

• replant but in pots so there is no mistaking it's deliberately planted.

• whether replanting in the earth or pots, put up a twee sign ("may all your weeds be wildflowers" etc to indicate its deliberate.

I wouldn't daub any wall whether yours or not as it looks passive aggressive and will inflame tensions.

Male a point of being friendly to them. Eye contact, hellos, a bit of forced chat. Generally people find it harder to do things that they know will piss off someone they regularly engage with (whether they like the chats or not 😆)

It sounds lovely, YANBU to be devastated. I would actually go round and have a chat with them - I'd worry they'd do it again if I didn't speak to them.

Not sure a passive aggressive mural is a very good idea, but maybe take the opportunity to scatter a wildflower mix or add some lovely poppies or whatever you like best while the ground is clear?