In my limited knowledge. With a contract, it depends on how long you have worked for your company. If they have not given you a contract to sign, by the fact that you have continued to work for them, means that in effect you have accepted the terms and conditions of your company. However, check on that in case I am wrong. I am an employer and use employment advisors. Sometimes I cannot get my employees to sign and return their contracts to me, but my advisors have given me the advice I have passed to you regarding the legality of my contracts. When it comes to flexible working, I believe the new rules only cover new parents and your employers have no legal duty to consider you for part time work, but this to me does seem unfair, especially if the stress of returning to work full time just makes you unwell again. This could be costly for both you and your employer if this happens again. It may be worth putting this point to them?
All the best, Sue.