In general a verbal or oral contract should have the same weight as a written contract. However, should a dispute arise, the nature of the contract is much more difficult to prove and it can become a case of your word against another's. It is never a bad idea to follow up such a verbal agreement with a letter of confirmation, stating briefly what was agreed. Post this by recorded mail and keep a copy. The other party should respond in writing that they accept the terms but, even if they don't, the fact that they received your letter and did not rebut the contents would help prove your case.