How can I get my money from ex-best friend builder?

Oh dear, where to start!! This so called friend of yours can't be much of a builder if he advised you to get cracking on an extension without planning permission. You were doomed from the start! It sounds like he was short of work and used you to fill a gap until something else came along. You don't have a leg to stand on to be honest. I would also suggest that you get the work checked that has already been done as my guess is its utter rubbish if this is the way he conducts business. Normally these guys take shortcuts beyond belief and as he has just carried the work out off his own back and had no inspections from building control I am pretty certain there will be problems!! Live and learn.

Hi, This is what I call the favour trap. You thought you were doing him a favour when he was out of work, he thought he was doing you a favour by doing the work cheaply. The problem with that type of relationship...where both sides feel that the other side owes them something for their gesture... is that it always, always end in tears. Problems with the elderly neighbour did not stop the build, problems with the house owners not having planning permission stopped the build. You have got what you paid for, nothing more, nothing less. You can't possibly believe that you have got a certain part of the whole job, when you do not even know what the whole job was. To throw away a friendship without knowing that, is brutal. The only sad thing here is that you have lost a friend, the rest is just money that you may have thrown away because you did not do the right thing. The right thing being, specification, quotation, planning, contracts. I work with my best mates all day every day, but business is business and there are no shortcuts that are worth any friendship. Sorry couldn't help any further