A verbal contract is just as enforceable as a written contract provided the terms are not in dispute.
Sometimes, a written contract will have a provisioning called a “whole agreement clause” which is a clause doing exactly what it says and says that this is the whole agreement unless anything is attached and in writing.
For there to be a contract there needs to be an offer and acceptance (verbal or written). If the acceptance is qualified such as when someone accepts it with a variation, that is not an acceptance but a counter offer which would be subject to further acceptance.
Any work carried out on a contract has to be carried out with reasonable care and skill under the terms of the earlier Supply of Goods and Services Act or the newer Consumer Rights Act. What is reasonable care and skill is a matter of fact. The main contractor is responsible to the customer and any subcontractors are responsible to the main contractor. The exception would be the subcontractor was engaged by the customer. It would be most unusual for a contractor or subcontractor to be paid for remedial work unless it was as a result of some defective instruction or change of requirements of the customer.
If you could explain your situation in more detail along with any matters arising I may be able to assist you further.
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