Does anyone else have an itinerary that would include a few castles, ancient ruins, thatched roofs, good pubs, charming b&b's coastline and of course wild horses. We would like to map as much of this out since we don't have long before we leave.
You can have this with a route along the South Coast even ending up in Cornwall if you wanted to.
You could start in Brighton or Arundel (taking a car from Heathrow or train to Brighton/Arundel and collecting a car from there) and visit Arundel Castle, it's not a ruin but a complete and well preserved castle http://www.arundelcastle.org
From there you can carry along the A27 towards Chichester for a bit of Roman history at Fishbourne Roman Palace https://sussexpast.co.uk/properties-to-discover/fishbourne-roman-palace
Chichester itself is very historic with a strong Roman past and an excellent cathedral.
If you wanted to view some bronze age burial mounds and the oldest yew forest in Britain then nearby Kingley Vale is a good place to visit. The climb can be a bit steep but the views at the top are amazing http://www.visitchichester.org/activity/kingley-vale-trail.
I would then recommend Portchester Castle on the outskirts of Portsmouth, an original Roman 'Saxon Shore' fort later updated by the Norman's. It's a very well preserved castle and one of my favourite places in the area to visit http://www.english-heritage.org.uk/visit/places/portchester-castle/
If you didn't want to visit Portsmouth (easily a whole day) then you could drive the short distance to the Royal Armouries Musuem at Fort Nelson (free entry) https://royalarmouries.org/venue/fort-nelson/ on your way to the picturesque village of Southwick with its plethora of thatched cottages and links to the D-Day invasion http://www.southwick-estate.co.uk.
I would then recommend making your way to the New Forest via the easily accessible M27. There are many places to stay within the forest and I would recommend visiting Bucklers Hard https://www.bucklershard.co.uk/attractions/, Beaulieu https://www.beaulieu.co.uk, Exbury Gardens https://www.exbury.co.uk and Hurst Castle http://www.hurstcastle.co.uk to name just a few! You will also experience wild ponies galore along with free roaming cattle, pigs and deer. There is a network of walking trails, cycling trails and guided tours of the forest.
After the forest you can head towards Bournemouth (I'd skip the town unless you want a taste of traditional English seaside resort) and head down towards Corfe Castle https://www.nationaltrust.org.uk/corfe-castle. A great ruin to explore with amazing views on a good day. You'll drive through plenty of pretty villages, many with thatched cottages. From here it's a short drive to the majestic Lulworth Cove and Durdle Door https://jurassiccoast.org/walkthroughtime/highlight-lulworth-cove-and-durdle-door/.
Heading west along the Devon coast you'll find plenty of small villages and hundreds of rental cottages, B&B's etc. The area around Lyme Regis is a popular place to stay (we've rented a lovely cottage in nearby Seatown previously) and the coast is an incredible area for fossil hunting.
From here you can carry on west into Cornwall or you could go North and visit the Cotswolds. My preference would be to carry on to Cornwall.
There are many more places to explore and sights to see along this route but this is a general overview and it depends on how long you want to stay in a particular place and how far you want to go. Of course it doesn't include the Lake District but it's just an idea of another part of the country that is often overlooked by foreign visitors.