Please
This is a simple one
Only a duly JAR qualified and current flying instructor can teach you to fly in the UK.
If your mate tries to teach you please refuse as he may be teaching you things in the wrong and potentially FATAL way!!
I know it's expensive but what price would you put on your life.
There are dozensof training schools around the country, walk into any one of them and you should get some good advise.
Good luck