cover the crown of the tree. What can I do to top up without damaging the tree? Tree is healthy and produces lemons. I have tried to lift the tree to add soil at the bottom, but it's way too heavy. Thank you.
You can remove the top 1/3 of the soil and replace it as suggested in this article:
https://www.gardeningknowhow.com/houseplants/hpgen/how-to-refresh-potted-plants.htm
as its roots are blocking a drain i have been told my drain man that there is no need to cut down the tree. it is directly beside my 130 year old red brick cottage and is there at least 35 years. If I did cut it down would there be subsidence when roots die?. I am happy to leave tree if it safe to do so as there are no cracks in the walls.
Actually, it might be better to move the shrub somewhere else, or remove it completely. The root system of this one is about 3 times the width of the canopy, and they do have a chance at damaging structures as they age. It would be better to let soil fill in the cavity left behind by decaying roots, naturally, then it would be to leave it to do damage. As well, your drains will get clogged again eventually. Keep in mind that some specimens can live to around 200 to 300 years, so it isn't very old, yet.