The law in the UK stands as this:

To record the conversation for your own listening only, then you do not need to notify the other person. If you intend for anyone but yourself to hear the recording, then you need to gain consent from the other party as per the Regulatory Investigave Powers Act:
http://www.legislation.gov.uk/ukpga/2000/23/section/1

Basically, if you are recording stuff to make sure you don't forget details, that's fine. If you are recording stuff to use in court (for example), then you have to notify the other party at the start of the conversation that you are recording it.