extension walls, both internal block and external brick laying not straight

hi ther seems like the corners arnt set up properly,also line band not been used ? the only way to correct this work is knock it down and start again cheers dave

knock down Or render over the brickwork?

Take it all down, get a decent builder/ brickie in.

If it really is that bad,did this guy get the foundations passed by building control at any point? If not then you might as well pull it all down.An extension like this will devalue your home.If it has approved foundations and is only single storey then you may be able to save the inner skin and just redo the face brickwork for appearance sake.This depends on a lot of things though such as whether you mean straight or upright and how far out these walls are.I have been to jobs like this is the past and scenarios vary from horrendous to not being able to find anything wrong with the work at all.My advice would be to list it as a job on here and get a few opinions before you bulldoze it.It really might not be that bad.

no other way it would have to be taken down and rebuilt

I agree with Roc. Get a couple of more reputable builders out to have a look at it and go from there. There may be an easy solution to the problem, but you may have to have it ripped down and started again from footings up!! The only way to be sure is to get the work checked. Rick