I have very recently bought an Allum plant and it looked quite healthy in our local nursery

Yes, there is yet hope. Did you have this plant in direct sun? It can't take direct sun - Sun to Partial Shade, Light Shade, Partial to Full Shade

I see what looks like scorching. Do you see how the leaves have curled edges burned.

Keep plant out of prolonged periods of direct sun. Early morning sun or evening sun is OK for an hour or two. I think it can be saved. Keep it watered. The damaged leaves will never recover - they are gone. As the plant regenerates, trim off the damaged leaves a little at a time.

The bone meal was not necessary. Be careful not to offset the PH of the soil; mildly acidic to mildly alkaline for this plant. This plant is fairly forgiving.

Was the arum under cover when you bought it? The weather in most of the UK has been so cold that if it was and you then planted it out the change in temperature could have caused this. As Bathgate says keep it watered and bone meal was not necessary however, I would not lift and replant as will only disturb. How big is the container the arum is in - looks a little small to me.

The container looks far too small to me. It would be much better in the open ground, part shade and kept moist.

Which Arum is it? The leaves of Arum maculatum are dying off now anyway, they've done their job.

Thank you all I will try to answer all questions.. yes it is in full sun quite hot in this corner as well so I will now move it to a more suitable area...yes it was under cover when bought and I do think the container is not big enough so I will bite the bullet there and move it...not sure of the type but it is the one with white trumpets. OK I can see the error of my ways and will try to put things right. Once again Thank You for your interest. Best Regards