It is not normally the case that a self employed person could be dismissed other than if he was in breach of the terms of his contract. An employee would have the right to be given statutory notice of the termination of his employment. HMRC see notice periods as being indicative of employment however reasonable notice periods are considered defendable.
If a contractor is not able to terminate their contract early, or has a notice period in excess of one month, this is likely to demonstrate that a mutuality of obligation does exist and is likely to weaken the contract.