Contact your local councillor immediately. It is what they are there for. Better still, get all your neighbours to contact them independently. Weight of numbers counts! You will be able to get their number from your Town Hall/County Council (whichever is appropriate). Also, try phoning the planning department and ask to speak to the officer dealing with the proposal (should be on the letter you had) and ask them to explain the decision in view of the objections. Your neighbour doesn't have to accept the planning permission. Ask him if he will build it to the revised (agreed?) layout.