Thank you both so much I really appreciate this. When I first brought the plant it was in a different position - it was quite close to a radiator and started losing all its leaves... so then I moved it to that corner and it does get sun light and started to regrow - I will move it again now and try a different spot.
I didn't repot the plant but I did dig up some of the soil and add in extra? As you can see the bottom of the tree is lovely and has new leaves coming! But I don't know what I should do with the top and whether I should chop off the dead branches?