Discussions

So I am planning to visit England, Scotland and maybe even Ireland next summer and was wondering if anyone has any advice on what is the best plan of action. I'm thinking of joining a tour group to visit all the hot spots in London and then taking a train to the Lake District and renting a car to make day trips to the places we want to go in northern England and southern Scotland. We will stay at B&Bs for the most part. Any advice or hints would be greatly appreciated. Also, when is the best time to go (not so busy, but still good weather).  
Thanks  
 
Oh and I will be talking to a travel agent, but I really want advice from those who have done it themselves.