If an employer agrees to a flexible working request, does it have to issue a new contract of employment to the employee?

If an employer agrees to a flexible working request, since the parties will be agreeing a change in terms and conditions of employment, the employer should issue a written statement of the change under s.4 of the Employment Rights Act 1996. Where the change is an extensive one, the employer may decide to issue a revised contract to the employee to avoid any confusion about what the new terms are, but there is no legal requirement to do this.