Can my employer force me to undertake/ agree to undertake an occupational health assessment? 

I have been working for my employer for just over 2 years. I had an occupational health assessment when I started my role and appropriate adjustments were eventually put in place after a long battle and having to provide over and above detail about how my disability effects me. In my previous role with this employer they once tried to revoke a number of adjustments without having a business reason. When I challenged this and one of their teams specialising in adjustments became involved, my employer told them that they wished to refer me to occupational health to try and find a business reason to withdraw the adjustments. I declined the referral and as they became aware that I would be moving roles within the near future they dropped the matter. 

I have since moved roles over a year ago and the adjustments have been in place without any problems. I have recently had to have another adjustment added without the need of an occupational health assessment. They initially referred me without consent and I obtained a copy of the referral in which they basically made out I didn't need the adjustment and they wanted occupational health to tell them why I needed it. I pointed out that I had already provided the reasons on several occasions and their team specialising again in adjustments became involved to reiterate to them that if they accepted my reasoning and the business could accommodate the adjustment it should be put in place without the referral. My manager accepted and it was put in place, however now he keeps making comments to me regarding the fact that he finds it funny that I was able to do my job without it for a year etc and that they are going to review having the adjustment in place every few months.  

I do not feel I need any other adjustments. I am not under any attendance management or performance procedures. I have recently secured a promotion which I am due to start in the next few weeks. The promotion is on the same team, broadly similar work as I will just be managing my current team and they have already stated that they can still accommodate my current adjustments. 

Unfortunately the manager (current and will be new line manager) who wasn't involved in the promotion and appointment exercise that is very unhappy that I have been given my new role and is of the opinion that someone with my disability (mental health - bi polar) should not manage a team. I have already asked what pre-appointment checks are carried out etc and none of this involves a standard occupational health referral. The manager has been attempting to get my appointment to the role revoked and has made a number of discriminatory comments to me in the process. He has been told by HR that this is not possible. HR have stated however that for business reasons they would be able to change the role I was given. At present they do not have a business reason. 

I am now being asked to undertake a occupational health assessment. Talking in detail about how my disability effects me upsets me greatly and past experience has shown that it triggers and episode of ill health. I have made this very clear to my employer. When I have asked HR of its purpose they have stated it is so that my manager can understand my disability better and this information needs to come from occupational health rather than directly from myself. I have asked if its not how the condition effects me personally, why he cannot simply research the condition himself or ask occupational health to give him a broad overview of the condition. They are still pushing for a referral but they have no real purpose other than general curiosity or I fear it is to try and find something which they could try and construct into a business reason why I cannot carry out my new role. 

Any advice on or off board would be greatly appreciated.