You will only be liable to inheritance tax if your uncles estate is worth over �300,000. If it is, then you wil be taxed at 40% of the excess over the �300,000. It can be a hefty tax.
Capital Gains Tax (CGT) is payable upoin disposal of an asset....such as stocks and shares.....some investments....antiques....other properties (but not the one he lives in) etc etc.....
An accountant can provide more in depth advice on CGT, but he/she will have to know exactly what your uncle has in assets.
With regard to Inheritance Tax....if your uncles health is failing now...then it may be already too late to plan for inheritance tax (I wont bore you with the details, but people generally have to survice 7 years for there not to be any inheritance tax after they have gifted some money/assets to you. You may, however want to encourage your uncle to seek advice from a solicitor who may be able to do someting with his will to help mitigate some inheritance tax.
Hope this helps...........