Communal garden, decking being added

[Plump82]

I live on the corner of 2 street which has a communal back garden. All houses that back on the garden own it and have full use of if. Have woke up this morning to see one of the neighbours looks to be having some decking put down outside their house. Is this allowed? Should they have not asked the other owner permission?

No, it won't be allowed. Who manages it?

It's just managed by the residents. There's no factor. 2 owners arrange for the grass to be cut etc and then we all pay them. Immediately outside people's flats/houses some have put flowers in etc which is no problem and then there's the "green" right in the middle.

Looks like you'll have to talk to these people as a group, then. Assuming all the others are in agreement.
It's a very cheeky thing to do without any by your leave.