I assume you are in europe ?
Sounds like youve been out of the FAA system for a while?
Well you need to do a Certified Flight Instructor (CFI) Licence test. Which you can use with your ATP licence.
If you do this in a single engine that will allow you to teach any licence in single engine aircraft. You can then add an MEI, to teach on twins or add a CFII to teach instrument ratings. You could also do a MEI first if you so desire.
Books- You should get a new copy of the FARs. FAR61, flight/ground req's are all there. A copy of recent practical test standards book (PTS) for which ever instructor tickets you decide to undertake. Pilots Handbook of Aeronautical knowledge and the Fundamentals of Instructions are both FAA publications which u can buy bound or download from faa.gov, you should know them as that is the req'd level of theoretical knowledge.
Then get some training from an approved instructor and a sign off for the written tests and the flight test.
I believe some written tests can be done somewhere in england ??
I m not sure about FAA designated pilot examiner availability in the UK, but might be an idea to travel to florida or somewhere for the flight test.
hope this gets u a start, feel free to fire anymore questions my way
