My findings are based on my own experiences. For example two hours of dual carriageway driving in my car gets you about 100 miles and a uses ⅓ of a tank, that works out as £12 in each direction. Two hours of driving will give you access to quite a lot of the Sussex or summerset coastline from London and the Thames Valley. Most train tickets to the coast cost more than £20 in each direction. Most cars have 5 seats so you can take the whole family with you.
If you have a hybrid or electric car then the difference in price is even greater.