leashold question

[jack99]

I am in the process of buying a flat with 73 years remaining on the lease (99 originally). I have never bought a leashold property before and was wondering ears if 73 years is a long enough period to have left on a lease and if I could have problems when I come to sell the flat. Also has anyone ever extended a lease on a property and if so was it expensive and difficult to do.
Any advice would be very much appreciated.