i had an archway put in my kithen wall (non lowbearing wall) to open it up to the dining room. Do you need building regs, and if so , what if the work has already been done

If it's definately not a load bearing wall then you could take the wall down completely without changing the structural integraty of the property so building regs will not apply and it will be fine. (on who's advice is it a non load bearing wall?) and if your not sure/confident of the reliability of this advice or no advice was given or sought, I strongly advise you seek proffessional advice immediately. If it is a load bearing wall, BUILDING REGS WILL APPLY, and if you have had the work carried out without you or the contractor that carried out the work getting the work inspected, you could be putting yourselves at serious risk if the works are inadequate making the propery unsafe to live in. It's normally the contractors job to see that all necessary inspections are carried out before, during and after works, again if your not sure, please seek proffessional advice immediately.

No building regs required for opening up a partition wall.