Going to England for First Time - 3 Weeks in Sept/Oct

My personal opinion is that trains are preferable when possible. They are so easy and the train station is often conveniently located. For Lake District and Cotswolds, and Cornwall car would be better.

consider flying in to Manchester, out of London, or vice versa. There are direct flight options from North America to Manchester.

You can access plenty of the English countryside - as well as all major towns and cities - by public transportation (trains and/or buses), so unless you have your heart set on a specific destination far off the beaten path, there's really no need to get a car at all. For long distances (e.g., London to York), the train is usually much faster than driving. And as you may already realize, in London, you're far better off NOT having a car.

You'll want to buy those train tickets in advance, though, because walk-up fares on many routes are extremely high.

For my first visit, I combined trains and buses. For my second, I did a mix of trains and car rental. You can get to many places faster by train than by car, and the buses will take you to lots of small towns as well. For the countryside (Lake District and Cotswold areas for example), you can take a train to the area and rent a car for a few days to drive in the country. You can take a train from London to Manchester in just over 2 hours, but driving takes almost 4 hours. From Manchester, you could rent a car to drive to the Lake District or take a train to the area and rent a car there. A car in scenic rural areas does give a bit more flexibility.

You could also take a train to Oxford and rent a car there to explore the countryside.

For many of the cities, driving and parking are difficult and expensive.

Up until today I had never even thought of the trains. After these suggestions I am rethinking how I am planning my trip and adding trains for sure. There is just soooo much information available it's making the planning a bit overwhelming. Thanks for the input.

When going from London (Euston) to Manchester or the Lake District, you will be using Virgin Trains - so it would be best to pre-book with them. I find www.nationalrail.co.uk to be the easiest way to find schedules & fares - click DETAILS for any change points. As has been said, pre-book specific train(s) for longer distance journeys about 11 weeks ahead to get the lowest prices. (Short trips - pay on the day).
https://www.virgintrains.co.uk

Direct trains also go from Manchester to The Lake District. You will also find that you can get relatively quickly form The Lake District to Edinburgh. Why not go Euston > Manchester; Manchester > Windermere (Lake District); maybe go by bus to Keswick for a stay and then bus to Penrith for train to Edinburgh (or Newcastle); then go from Edinburgh to Newcastle to York; finally, York to London (Kings Cross). For buses:> www.traveline.info
http://www.lakedistrict.gov.uk/visiting
https://www.visitscotland.com/destinations-maps/edinburgh-lothians/
http://www.visityork.org/?AskRedirect=true

I enjoy driving, so I find rural driving is fun and city driving is miserable. Consider something like this:

Multi-city ticket with arrival in Manchester and departure from London. See Manchester with no car. Then by rail to your next destination. If that's a region like the Lake District, using a car for the duration of your stay there will give you flexibility compared to relying on buses, etc.

If your destination is a city, however, say York, you won't need a car unless/until you want to explore the outlying areas.

With 3 weeks, I can see you regularly combining trains/buses and city stays and car rentals for explorations outside cities, e.g. Cotswolds, Yorkshire, etc.

London, then, comes at the end of your visit. Take a train in from wherever you find yourself. If your departing flight is in the morning, consider spending the last night in an airport hotel to save some time and hassle.

Read up here and elsewhere on U.K. rail/bus pricing systems.