yes. you are just charging the consultant a referral commission yes? and that they invoice the client direct and the client pays them direct?
Id say that you need to establish that your s/e are hired by you on the basis that they meet HMRC regs for s/e. ie you cannot determine their days or hours worked, cannot train them, pay them holidays, sick, etc. stuff like that.
Once you have determined your s/e meet that criteria (HMRC can confirm this for you) then just make sure this is made clear to both parties in T & C.
Then, they are responsible for their own liability in all respects, as they are not employed by you. You need a disclaimer with the client that you are not responsible for th s/e person. Make sure your T & C are approved by a lawyer if not done so already.
I am presuming you are a Ltd company? In which case you need employers liability anyway. Even if you don't actually employ any one, it provides cover for any thing your company may do wrong. I have been through this with a broker as we used to take on self employed drivers, they would sub-contract for us on jobs. We had to have employers liability by law to cover us & them, but they had to have the own public liability to cover any incidents away from the office.
Hope this makes some sort of sense!