Last night I went to the SCL's National Liberal Club talk on these topics. English law does not have a stand alone duty of good faith. Moreover, a fundamental building block in English law is freedom of contract so it can be unclear how good faith fits into that. The courts are slow to pick apart commercial terms and/or savvy and reasonable commercial standards simply because a contract says the parties "shall act in good faith" or because the parties have been contracting over a long period of time. Nonetheless standard form construction contracts still contain wording such as the parties shall act with "mutual trust and confidence". 

My key take home from last night is: if you want to create an ethos of good faith and/or relational contracting, a mere nod to that with some peppering of clauses relating to this will not be enough. Consider how to create that ethos with the team towards a common goal and get the contract terms to reflect that. Moreover, be careful about standard amendments that might conflict with the ethos you are trying to achieve. Best to seek legal advice about your goals so these can be reflected accordingly.