My next door neighbours (I'm in a mid terrace so attached to them as well as other side!) had a big old extension built summer before last. It managed to take about 18 months somehow!
It was allowed under "permitted development" rules, so there was little I could do to comment on it, let alone stop it.
They had had a flat roof tiny extension beforehand which was demolished, and new one is allegedly still single storey but with massive high ceiling so it manages to block all of my light/sky. Plus I get all their noise and kitchen stinks through the oven hood vent which blows right in to my garden...
But I'm not bitter about the whole experience at all!
Now re the vent my friend is having a similar problem and the council is involved. They are trying to get them to voluntarily attach something that will vent the smells up. Next door but one to us has for the last 12 months been converting a 4 bed into a 6 bed 6 bath house for 3 families. The pile of rubbish on the front gets bigger and hubby is going to find our union flag and stick it in the top.!!!! Complaints to the council don't seem to have had any effect.