My 84-year old (UK born) mother owns a flat in London with a market value of around 300,000 GBP. She has lived in New York for about 50 years and has both US and UK citizenship. She uses the flat when she visits London, but otherwise it is un-occupied. She is now considering selling it, but we are also wondering about the consequences if she sells it, or is it better for me to buy it from her and keep the flat? Our main concern is avoiding inheritance taxes, if applicable in her case (and how much would the taxes be?), but I am also interested in keeping the apartment as it is a prime property. Please advise what would be the best and wisest thing to do in this situation.

Having been in the USA for the past 50 years, it is most likely that your mother has abandoned her UK domicile of origin, and has now acquired a USA domicile of choice. See http://hmrc.gov.uk/manuals/rdrmmanual/RDRM22000.htm. If so, she is only liable to UK inheritance tax (IHT) on her UK located assets. If these amount to less than £325,000 then there is no IHT. If all she has in the UK is her flat worth £300,000 then there is nothing to talk about. She should hold on to it until she dies and then you can inherit it without any UK capital gains tax. If she has bank accounts here, or other assets, maybe it is worth considering moving them out of the UK, in order to avoid UK IHT. Your mother should also seek advice from a US tax specialist on any US tax implications of this scenario.