I am due to return from maternity leave in mid-March but have opted to take annual leave until mid April. My employer has issued me a new contract (my existing one expires end of March) and the new contract is permanent. They have however made a substantial change in the contract and instead of having a clause of non soliciting clients for 6 months they are now effectively barring me from working in the same industry for 12 months after leaving my company. I have asked them to change/delete this clause as really struggle to see how I could be seen a 'critical' person (I work in admin). If they refuse to change the clause and insist I am indeed a critical person, what are my chances of claiming constructive dismissal based on the fact that my terms and conditions have changed substantially? I have no intention of working at Tesco for 12 months and will not sign such contract.