Once an employer has made you an offer of employment (usually with by offer letter) and you have accepted that offer in writing there will usually be a binding legal agreement even where the job is yet to start, you have done no work and you have received no salary.
If you want to pull out of the employment after you have accepted it, contractual notice will usually be required. If you give that contractual notice and it runs out before your new employment is due to start there will be no breach of contract by you and nothing will be payable.
If notice is still running and you refuse to work from the start date you will be in breach of contract. The employer could sue you for breach of contract for any loss it suffers as a result of your breach – from the start date to when your notice expires. There may be no easily quantifiable loss for the employer to sue you for. But please note that the more senior or specialist you are and the longer the period of notice still to run after the start date when you give notice, the more likely that there could be substantial quantifiable loss which the employer may want to try and recover from you.
This article/blog is for reference purposes only. It does not constitute legal advice and should not be relied upon as such. Specific legal advice about your specific circumstances should always be sought separately before taking or deciding not to take any action.