Most employment contracts do not need to be in writing to be legally valid, but it is better if they are.
A contract 'starts' as soon as an offer of employment is accepted. Starting work proves that you accept the terms and conditions offered by the employer.
Most employees are legally entitled to a Written Statement of the main terms and conditions of employment, within two calendar months of starting work. This should include details of things like pay, holidays and working hours.
An existing contract of employment can be varied only with the agreement of both parties.
MTM can provide you with a suitable Written Statement of Employment for your employees and provide you with Employment Law support services.